RFC 3501

Network Working Group M. Crispin
Request for Comments: 3501 University of Washington
Obsoletes: 2060 March 2003
Category: Standards Track
INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Internet Message Access Protocol, Version 4rev1 (IMAP4rev1)
allows a client to access and manipulate electronic mail messages on
a server. IMAP4rev1 permits manipulation of mailboxes (remote
message folders) in a way that is functionally equivalent to local
folders. IMAP4rev1 also provides the capability for an offline
client to resynchronize with the server.
IMAP4rev1 includes operations for creating, deleting, and renaming
mailboxes, checking for new messages, permanently removing messages,
setting and clearing flags, RFC 2822 and RFC 2045 parsing, searching,
and selective fetching of message attributes, texts, and portions
thereof. Messages in IMAP4rev1 are accessed by the use of numbers.
These numbers are either message sequence numbers or unique
identifiers.
IMAP4rev1 supports a single server. A mechanism for accessing
configuration information to support multiple IMAP4rev1 servers is
discussed in RFC 2244.
IMAP4rev1 does not specify a means of posting mail; this function is
handled by a mail transfer protocol such as RFC 2821.
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8. Sample IMAP4rev1 connection ............................ 80
9. Formal Syntax .......................................... 81
10. Author's Note .......................................... 92
11. Security Considerations ................................ 92
11.1. STARTTLS Security Considerations ....................... 92
11.2. Other Security Considerations .......................... 93
12. IANA Considerations .................................... 94
Appendices ..................................................... 95
A. References ............................................. 95
B. Changes from RFC 2060 .................................. 97
C. Key Word Index ......................................... 103
Author's Address ............................................... 107
Full Copyright Statement ....................................... 108
IMAP4rev1 Protocol Specification
1. How to Read This Document
1.1. Organization of This Document
This document is written from the point of view of the implementor of
an IMAP4rev1 client or server. Beyond the protocol overview in
section 2, it is not optimized for someone trying to understand the
operation of the protocol. The material in sections 3 through 5
provides the general context and definitions with which IMAP4rev1
operates.
Sections 6, 7, and 9 describe the IMAP commands, responses, and
syntax, respectively. The relationships among these are such that it
is almost impossible to understand any of them separately. In
particular, do not attempt to deduce command syntax from the command
section alone; instead refer to the Formal Syntax section.
1.2. Conventions Used in This Document
"Conventions" are basic principles or procedures. Document
conventions are noted in this section.
In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "MAY", and "OPTIONAL" in this document are to
be interpreted as described in [KEYWORDS].
The word "can" (not "may") is used to refer to a possible
circumstance or situation, as opposed to an optional facility of the
protocol.
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"User" is used to refer to a human user, whereas "client" refers to
the software being run by the user.
"Connection" refers to the entire sequence of client/server
interaction from the initial establishment of the network connection
until its termination.
"Session" refers to the sequence of client/server interaction from
the time that a mailbox is selected (SELECT or EXAMINE command) until
the time that selection ends (SELECT or EXAMINE of another mailbox,
CLOSE command, or connection termination).
Characters are 7-bit US-ASCII unless otherwise specified. Other
character sets are indicated using a "CHARSET", as described in
[MIME-IMT] and defined in [CHARSET]. CHARSETs have important
additional semantics in addition to defining character set; refer to
these documents for more detail.
There are several protocol conventions in IMAP. These refer to
aspects of the specification which are not strictly part of the IMAP
protocol, but reflect generally-accepted practice. Implementations
need to be aware of these conventions, and avoid conflicts whether or
not they implement the convention. For example, "&" may not be used
as a hierarchy delimiter since it conflicts with the Mailbox
International Naming Convention, and other uses of "&" in mailbox
names are impacted as well.
1.3. Special Notes to Implementors
Implementors of the IMAP protocol are strongly encouraged to read the
IMAP implementation recommendations document [IMAP-IMPLEMENTATION] in
conjunction with this document, to help understand the intricacies of
this protocol and how best to build an interoperable product.
IMAP4rev1 is designed to be upwards compatible from the [IMAP2] and
unpublished IMAP2bis protocols. IMAP4rev1 is largely compatible with
the IMAP4 protocol described in RFC 1730; the exception being in
certain facilities added in RFC 1730 that proved problematic and were
subsequently removed. In the course of the evolution of IMAP4rev1,
some aspects in the earlier protocols have become obsolete. Obsolete
commands, responses, and data formats which an IMAP4rev1
implementation can encounter when used with an earlier implementation
are described in [IMAP-OBSOLETE].
Other compatibility issues with IMAP2bis, the most common variant of
the earlier protocol, are discussed in [IMAP-COMPAT]. A full
discussion of compatibility issues with rare (and presumed extinct)
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variants of [IMAP2] is in [IMAP-HISTORICAL]; this document is
primarily of historical interest.
IMAP was originally developed for the older [RFC-822] standard, and
as a consequence several fetch items in IMAP incorporate "RFC822" in
their name. With the exception of RFC822.SIZE, there are more modern
replacements; for example, the modern version of RFC822.HEADER is
BODY.PEEK[HEADER]. In all cases, "RFC822" should be interpreted as a
reference to the updated [RFC-2822] standard.
2. Protocol Overview
2.1. Link Level
The IMAP4rev1 protocol assumes a reliable data stream such as that
provided by TCP. When TCP is used, an IMAP4rev1 server listens on
port 143.
2.2. Commands and Responses
An IMAP4rev1 connection consists of the establishment of a
client/server network connection, an initial greeting from the
server, and client/server interactions. These client/server
interactions consist of a client command, server data, and a server
completion result response.
All interactions transmitted by client and server are in the form of
lines, that is, strings that end with a CRLF. The protocol receiver
of an IMAP4rev1 client or server is either reading a line, or is
reading a sequence of octets with a known count followed by a line.
2.2.1. Client Protocol Sender and Server Protocol Receiver
The client command begins an operation. Each client command is
prefixed with an identifier (typically a short alphanumeric string,
e.g., A0001, A0002, etc.) called a "tag". A different tag is
generated by the client for each command.
Clients MUST follow the syntax outlined in this specification
strictly. It is a syntax error to send a command with missing or
extraneous spaces or arguments.
There are two cases in which a line from the client does not
represent a complete command. In one case, a command argument is
quoted with an octet count (see the description of literal in String
under Data Formats); in the other case, the command arguments require
server feedback (see the AUTHENTICATE command). In either case, the
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server sends a command continuation request response if it is ready
for the octets (if appropriate) and the remainder of the command.
This response is prefixed with the token "+".
Note: If instead, the server detected an error in the
command, it sends a BAD completion response with a tag
matching the command (as described below) to reject the
command and prevent the client from sending any more of the
command.
It is also possible for the server to send a completion
response for some other command (if multiple commands are
in progress), or untagged data. In either case, the
command continuation request is still pending; the client
takes the appropriate action for the response, and reads
another response from the server. In all cases, the client
MUST send a complete command (including receiving all
command continuation request responses and command
continuations for the command) before initiating a new
command.
The protocol receiver of an IMAP4rev1 server reads a command line
from the client, parses the command and its arguments, and transmits
server data and a server command completion result response.
2.2.2. Server Protocol Sender and Client Protocol Receiver
Data transmitted by the server to the client and status responses
that do not indicate command completion are prefixed with the token
"*", and are called untagged responses.
Server data MAY be sent as a result of a client command, or MAY be
sent unilaterally by the server. There is no syntactic difference
between server data that resulted from a specific command and server
data that were sent unilaterally.
The server completion result response indicates the success or
failure of the operation. It is tagged with the same tag as the
client command which began the operation. Thus, if more than one
command is in progress, the tag in a server completion response
identifies the command to which the response applies. There are
three possible server completion responses: OK (indicating success),
NO (indicating failure), or BAD (indicating a protocol error such as
unrecognized command or command syntax error).
Servers SHOULD enforce the syntax outlined in this specification
strictly. Any client command with a protocol syntax error, including
(but not limited to) missing or extraneous spaces or arguments,
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SHOULD be rejected, and the client given a BAD server completion
response.
The protocol receiver of an IMAP4rev1 client reads a response line
from the server. It then takes action on the response based upon the
first token of the response, which can be a tag, a "*", or a "+".
A client MUST be prepared to accept any server response at all times.
This includes server data that was not requested. Server data SHOULD
be recorded, so that the client can reference its recorded copy
rather than sending a command to the server to request the data. In
the case of certain server data, the data MUST be recorded.
This topic is discussed in greater detail in the Server Responses
section.
2.3. Message Attributes
In addition to message text, each message has several attributes
associated with it. These attributes can be retrieved individually
or in conjunction with other attributes or message texts.
2.3.1. Message Numbers
Messages in IMAP4rev1 are accessed by one of two numbers; the unique
identifier or the message sequence number.
2.3.1.1. Unique Identifier (UID) Message Attribute
A 32-bit value assigned to each message, which when used with the
unique identifier validity value (see below) forms a 64-bit value
that MUST NOT refer to any other message in the mailbox or any
subsequent mailbox with the same name forever. Unique identifiers
are assigned in a strictly ascending fashion in the mailbox; as each
message is added to the mailbox it is assigned a higher UID than the
message(s) which were added previously. Unlike message sequence
numbers, unique identifiers are not necessarily contiguous.
The unique identifier of a message MUST NOT change during the
session, and SHOULD NOT change between sessions. Any change of
unique identifiers between sessions MUST be detectable using the
UIDVALIDITY mechanism discussed below. Persistent unique identifiers
are required for a client to resynchronize its state from a previous
session with the server (e.g., disconnected or offline access
clients); this is discussed further in [IMAP-DISC].
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Associated with every mailbox are two values which aid in unique
identifier handling: the next unique identifier value and the unique
identifier validity value.
The next unique identifier value is the predicted value that will be
assigned to a new message in the mailbox. Unless the unique
identifier validity also changes (see below), the next unique
identifier value MUST have the following two characteristics. First,
the next unique identifier value MUST NOT change unless new messages
are added to the mailbox; and second, the next unique identifier
value MUST change whenever new messages are added to the mailbox,
even if those new messages are subsequently expunged.
Note: The next unique identifier value is intended to
provide a means for a client to determine whether any
messages have been delivered to the mailbox since the
previous time it checked this value. It is not intended to
provide any guarantee that any message will have this
unique identifier. A client can only assume, at the time
that it obtains the next unique identifier value, that
messages arriving after that time will have a UID greater
than or equal to that value.
The unique identifier validity value is sent in a UIDVALIDITY
response code in an OK untagged response at mailbox selection time.
If unique identifiers from an earlier session fail to persist in this
session, the unique identifier validity value MUST be greater than
the one used in the earlier session.
Note: Ideally, unique identifiers SHOULD persist at all
times. Although this specification recognizes that failure
to persist can be unavoidable in certain server
environments, it STRONGLY ENCOURAGES message store
implementation techniques that avoid this problem. For
example:
1) Unique identifiers MUST be strictly ascending in the
mailbox at all times. If the physical message store is
re-ordered by a non-IMAP agent, this requires that the
unique identifiers in the mailbox be regenerated, since
the former unique identifiers are no longer strictly
ascending as a result of the re-ordering.
2) If the message store has no mechanism to store unique
identifiers, it must regenerate unique identifiers at
each session, and each session must have a unique
UIDVALIDITY value.
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3) If the mailbox is deleted and a new mailbox with the
same name is created at a later date, the server must
either keep track of unique identifiers from the
previous instance of the mailbox, or it must assign a
new UIDVALIDITY value to the new instance of the
mailbox. A good UIDVALIDITY value to use in this case
is a 32-bit representation of the creation date/time of
the mailbox. It is alright to use a constant such as
1, but only if it guaranteed that unique identifiers
will never be reused, even in the case of a mailbox
being deleted (or renamed) and a new mailbox by the
same name created at some future time.
4) The combination of mailbox name, UIDVALIDITY, and UID
must refer to a single immutable message on that server
forever. In particular, the internal date, [RFC-2822]
size, envelope, body structure, and message texts
(RFC822, RFC822.HEADER, RFC822.TEXT, and all BODY[...]
fetch data items) must never change. This does not
include message numbers, nor does it include attributes
that can be set by a STORE command (e.g., FLAGS).
2.3.1.2. Message Sequence Number Message Attribute
A relative position from 1 to the number of messages in the mailbox.
This position MUST be ordered by ascending unique identifier. As
each new message is added, it is assigned a message sequence number
that is 1 higher than the number of messages in the mailbox before
that new message was added.
Message sequence numbers can be reassigned during the session. For
example, when a message is permanently removed (expunged) from the
mailbox, the message sequence number for all subsequent messages is
decremented. The number of messages in the mailbox is also
decremented. Similarly, a new message can be assigned a message
sequence number that was once held by some other message prior to an
expunge.
In addition to accessing messages by relative position in the
mailbox, message sequence numbers can be used in mathematical
calculations. For example, if an untagged "11 EXISTS" is received,
and previously an untagged "8 EXISTS" was received, three new
messages have arrived with message sequence numbers of 9, 10, and 11.
Another example, if message 287 in a 523 message mailbox has UID
12345, there are exactly 286 messages which have lesser UIDs and 236
messages which have greater UIDs.
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2.3.2. Flags Message Attribute
A list of zero or more named tokens associated with the message. A
flag is set by its addition to this list, and is cleared by its
removal. There are two types of flags in IMAP4rev1. A flag of
either type can be permanent or session-only.
A system flag is a flag name that is pre-defined in this
specification. All system flags begin with "\". Certain system
flags (\Deleted and \Seen) have special semantics described
elsewhere. The currently-defined system flags are:
\Seen
Message has been read
\Answered
Message has been answered
\Flagged
Message is "flagged" for urgent/special attention
\Deleted
Message is "deleted" for removal by later EXPUNGE
\Draft
Message has not completed composition (marked as a draft).
\Recent
Message is "recently" arrived in this mailbox. This session
is the first session to have been notified about this
message; if the session is read-write, subsequent sessions
will not see \Recent set for this message. This flag can not
be altered by the client.
If it is not possible to determine whether or not this
session is the first session to be notified about a message,
then that message SHOULD be considered recent.
If multiple connections have the same mailbox selected
simultaneously, it is undefined which of these connections
will see newly-arrived messages with \Recent set and which
will see it without \Recent set.
A keyword is defined by the server implementation. Keywords do not
begin with "\". Servers MAY permit the client to define new keywords
in the mailbox (see the description of the PERMANENTFLAGS response
code for more information).
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A flag can be permanent or session-only on a per-flag basis.
Permanent flags are those which the client can add or remove from the
message flags permanently; that is, concurrent and subsequent
sessions will see any change in permanent flags. Changes to session
flags are valid only in that session.
Note: The \Recent system flag is a special case of a
session flag. \Recent can not be used as an argument in a
STORE or APPEND command, and thus can not be changed at
all.
2.3.3. Internal Date Message Attribute
The internal date and time of the message on the server. This
is not the date and time in the [RFC-2822] header, but rather a
date and time which reflects when the message was received. In
the case of messages delivered via [SMTP], this SHOULD be the
date and time of final delivery of the message as defined by
[SMTP]. In the case of messages delivered by the IMAP4rev1 COPY
command, this SHOULD be the internal date and time of the source
message. In the case of messages delivered by the IMAP4rev1
APPEND command, this SHOULD be the date and time as specified in
the APPEND command description. All other cases are
implementation defined.
2.3.4. [RFC-2822] Size Message Attribute
The number of octets in the message, as expressed in [RFC-2822]
format.
2.3.5. Envelope Structure Message Attribute
A parsed representation of the [RFC-2822] header of the message.
Note that the IMAP Envelope structure is not the same as an
[SMTP] envelope.
2.3.6. Body Structure Message Attribute
A parsed representation of the [MIME-IMB] body structure
information of the message.
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2.4. Message Texts
In addition to being able to fetch the full [RFC-2822] text of a
message, IMAP4rev1 permits the fetching of portions of the full
message text. Specifically, it is possible to fetch the
[RFC-2822] message header, [RFC-2822] message body, a [MIME-IMB]
body part, or a [MIME-IMB] header.
3. State and Flow Diagram
Once the connection between client and server is established, an
IMAP4rev1 connection is in one of four states. The initial
state is identified in the server greeting. Most commands are
only valid in certain states. It is a protocol error for the
client to attempt a command while the connection is in an
inappropriate state, and the server will respond with a BAD or
NO (depending upon server implementation) command completion
result.
3.1. Not Authenticated State
In the not authenticated state, the client MUST supply
authentication credentials before most commands will be
permitted. This state is entered when a connection starts
unless the connection has been pre-authenticated.
3.2. Authenticated State
In the authenticated state, the client is authenticated and MUST
select a mailbox to access before commands that affect messages
will be permitted. This state is entered when a
pre-authenticated connection starts, when acceptable
authentication credentials have been provided, after an error in
selecting a mailbox, or after a successful CLOSE command.
3.3. Selected State
In a selected state, a mailbox has been selected to access.
This state is entered when a mailbox has been successfully
selected.
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3.4. Logout State
In the logout state, the connection is being terminated. This
state can be entered as a result of a client request (via the
LOGOUT command) or by unilateral action on the part of either
the client or server.
If the client requests the logout state, the server MUST send an
untagged BYE response and a tagged OK response to the LOGOUT
command before the server closes the connection; and the client
MUST read the tagged OK response to the LOGOUT command before
the client closes the connection.
A server MUST NOT unilaterally close the connection without
sending an untagged BYE response that contains the reason for
having done so. A client SHOULD NOT unilaterally close the
connection, and instead SHOULD issue a LOGOUT command. If the
server detects that the client has unilaterally closed the
connection, the server MAY omit the untagged BYE response and
simply close its connection.
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4. Data Formats
IMAP4rev1 uses textual commands and responses. Data in
IMAP4rev1 can be in one of several forms: atom, number, string,
parenthesized list, or NIL. Note that a particular data item
may take more than one form; for example, a data item defined as
using "astring" syntax may be either an atom or a string.
4.1. Atom
An atom consists of one or more non-special characters.
4.2. Number
A number consists of one or more digit characters, and
represents a numeric value.
4.3. String
A string is in one of two forms: either literal or quoted
string. The literal form is the general form of string. The
quoted string form is an alternative that avoids the overhead of
processing a literal at the cost of limitations of characters
which may be used.
A literal is a sequence of zero or more octets (including CR and
LF), prefix-quoted with an octet count in the form of an open
brace ("{"), the number of octets, close brace ("}"), and CRLF.
In the case of literals transmitted from server to client, the
CRLF is immediately followed by the octet data. In the case of
literals transmitted from client to server, the client MUST wait
to receive a command continuation request (described later in
this document) before sending the octet data (and the remainder
of the command).
A quoted string is a sequence of zero or more 7-bit characters,
excluding CR and LF, with double quote (<">) characters at each
end.
The empty string is represented as either "" (a quoted string
with zero characters between double quotes) or as {0} followed
by CRLF (a literal with an octet count of 0).
Note: Even if the octet count is 0, a client transmitting a
literal MUST wait to receive a command continuation request.
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4.3.1. 8-bit and Binary Strings
8-bit textual and binary mail is supported through the use of a
[MIME-IMB] content transfer encoding. IMAP4rev1 implementations MAY
transmit 8-bit or multi-octet characters in literals, but SHOULD do
so only when the [CHARSET] is identified.
Although a BINARY body encoding is defined, unencoded binary strings
are not permitted. A "binary string" is any string with NUL
characters. Implementations MUST encode binary data into a textual
form, such as BASE64, before transmitting the data. A string with an
excessive amount of CTL characters MAY also be considered to be
binary.
4.4. Parenthesized List
Data structures are represented as a "parenthesized list"; a sequence
of data items, delimited by space, and bounded at each end by
parentheses. A parenthesized list can contain other parenthesized
lists, using multiple levels of parentheses to indicate nesting.
The empty list is represented as () -- a parenthesized list with no
members.
4.5. NIL
The special form "NIL" represents the non-existence of a particular
data item that is represented as a string or parenthesized list, as
distinct from the empty string "" or the empty parenthesized list ().
Note: NIL is never used for any data item which takes the
form of an atom. For example, a mailbox name of "NIL" is a
mailbox named NIL as opposed to a non-existent mailbox
name. This is because mailbox uses "astring" syntax which
is an atom or a string. Conversely, an addr-name of NIL is
a non-existent personal name, because addr-name uses
"nstring" syntax which is NIL or a string, but never an
atom.
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5. Operational Considerations
The following rules are listed here to ensure that all IMAP4rev1
implementations interoperate properly.
5.1. Mailbox Naming
Mailbox names are 7-bit. Client implementations MUST NOT attempt to
create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox
names returned by LIST or LSUB as UTF-8. Server implementations
SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT
return 8-bit mailbox names in LIST or LSUB. See section 5.1.3 for
more information on how to represent non-ASCII mailbox names.
Note: 8-bit mailbox names were undefined in earlier
versions of this protocol. Some sites used a local 8-bit
character set to represent non-ASCII mailbox names. Such
usage is not interoperable, and is now formally deprecated.
The case-insensitive mailbox name INBOX is a special name reserved to
mean "the primary mailbox for this user on this server". The
interpretation of all other names is implementation-dependent.
In particular, this specification takes no position on case
sensitivity in non-INBOX mailbox names. Some server implementations
are fully case-sensitive; others preserve case of a newly-created
name but otherwise are case-insensitive; and yet others coerce names
to a particular case. Client implementations MUST interact with any
of these. If a server implementation interprets non-INBOX mailbox
names as case-insensitive, it MUST treat names using the
international naming convention specially as described in section
5.1.3.
There are certain client considerations when creating a new mailbox
name:
1) Any character which is one of the atom-specials (see the Formal
Syntax) will require that the mailbox name be represented as a
quoted string or literal.
2) CTL and other non-graphic characters are difficult to represent
in a user interface and are best avoided.
3) Although the list-wildcard characters ("%" and "*") are valid
in a mailbox name, it is difficult to use such mailbox names
with the LIST and LSUB commands due to the conflict with
wildcard interpretation.
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4) Usually, a character (determined by the server implementation)
is reserved to delimit levels of hierarchy.
5) Two characters, "#" and "&", have meanings by convention, and
should be avoided except when used in that convention.
5.1.1. Mailbox Hierarchy Naming
If it is desired to export hierarchical mailbox names, mailbox names
MUST be left-to-right hierarchical using a single character to
separate levels of hierarchy. The same hierarchy separator character
is used for all levels of hierarchy within a single name.
5.1.2. Mailbox Namespace Naming Convention
By convention, the first hierarchical element of any mailbox name
which begins with "#" identifies the "namespace" of the remainder of
the name. This makes it possible to disambiguate between different
types of mailbox stores, each of which have their own namespaces.
For example, implementations which offer access to USENET
newsgroups MAY use the "#news" namespace to partition the
USENET newsgroup namespace from that of other mailboxes.
Thus, the comp.mail.misc newsgroup would have a mailbox
name of "#news.comp.mail.misc", and the name
"comp.mail.misc" can refer to a different object (e.g., a
user's private mailbox).
5.1.3. Mailbox International Naming Convention
By convention, international mailbox names in IMAP4rev1 are specified
using a modified version of the UTF-7 encoding described in [UTF-7].
Modified UTF-7 may also be usable in servers that implement an
earlier version of this protocol.
In modified UTF-7, printable US-ASCII characters, except for "&",
represent themselves; that is, characters with octet values 0x20-0x25
and 0x27-0x7e. The character "&" (0x26) is represented by the
two-octet sequence "&-".
All other characters (octet values 0x00-0x1f and 0x7f-0xff) are
represented in modified BASE64, with a further modification from
[UTF-7] that "," is used instead of "/". Modified BASE64 MUST NOT be
used to represent any printing US-ASCII character which can represent
itself.
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"&" is used to shift to modified BASE64 and "-" to shift back to
US-ASCII. There is no implicit shift from BASE64 to US-ASCII, and
null shifts ("-&" while in BASE64; note that "&-" while in US-ASCII
means "&") are not permitted. However, all names start in US-ASCII,
and MUST end in US-ASCII; that is, a name that ends with a non-ASCII
ISO-10646 character MUST end with a "-").
The purpose of these modifications is to correct the following
problems with UTF-7:
1) UTF-7 uses the "+" character for shifting; this conflicts with
the common use of "+" in mailbox names, in particular USENET
newsgroup names.
2) UTF-7's encoding is BASE64 which uses the "/" character; this
conflicts with the use of "/" as a popular hierarchy delimiter.
3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
the use of "\" as a popular hierarchy delimiter.
4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
the use of "~" in some servers as a home directory indicator.
5) UTF-7 permits multiple alternate forms to represent the same
string; in particular, printable US-ASCII characters can be
represented in encoded form.
Although modified UTF-7 is a convention, it establishes certain
requirements on server handling of any mailbox name with an
embedded "&" character. In particular, server implementations
MUST preserve the exact form of the modified BASE64 portion of a
modified UTF-7 name and treat that text as case-sensitive, even if
names are otherwise case-insensitive or case-folded.
Server implementations SHOULD verify that any mailbox name with an
embedded "&" character, used as an argument to CREATE, is: in the
correctly modified UTF-7 syntax, has no superfluous shifts, and
has no encoding in modified BASE64 of any printing US-ASCII
character which can represent itself. However, client
implementations MUST NOT depend upon the server doing this, and
SHOULD NOT attempt to create a mailbox name with an embedded "&"
character unless it complies with the modified UTF-7 syntax.
Server implementations which export a mail store that does not
follow the modified UTF-7 convention MUST convert to modified
UTF-7 any mailbox name that contains either non-ASCII characters
or the "&" character.
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For example, here is a mailbox name which mixes English,
Chinese, and Japanese text:
~peter/mail/&U,BTFw-/&ZeVnLIqe-
For example, the string "&Jjo!" is not a valid mailbox
name because it does not contain a shift to US-ASCII
before the "!". The correct form is "&Jjo-!". The
string "&U,BTFw-&ZeVnLIqe-" is not permitted because it
contains a superfluous shift. The correct form is
"&U,BTF2XlZyyKng-".
5.2. Mailbox Size and Message Status Updates
At any time, a server can send data that the client did not request.
Sometimes, such behavior is REQUIRED. For example, agents other than
the server MAY add messages to the mailbox (e.g., new message
delivery), change the flags of the messages in the mailbox (e.g.,
simultaneous access to the same mailbox by multiple agents), or even
remove messages from the mailbox. A server MUST send mailbox size
updates automatically if a mailbox size change is observed during the
processing of a command. A server SHOULD send message flag updates
automatically, without requiring the client to request such updates
explicitly.
Special rules exist for server notification of a client about the
removal of messages to prevent synchronization errors; see the
description of the EXPUNGE response for more detail. In particular,
it is NOT permitted to send an EXISTS response that would reduce the
number of messages in the mailbox; only the EXPUNGE response can do
this.
Regardless of what implementation decisions a client makes on
remembering data from the server, a client implementation MUST record
mailbox size updates. It MUST NOT assume that any command after the
initial mailbox selection will return the size of the mailbox.
5.3. Response when no Command in Progress
Server implementations are permitted to send an untagged response
(except for EXPUNGE) while there is no command in progress. Server
implementations that send such responses MUST deal with flow control
considerations. Specifically, they MUST either (1) verify that the
size of the data does not exceed the underlying transport's available
window size, or (2) use non-blocking writes.
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5.4. Autologout Timer
If a server has an inactivity autologout timer, the duration of that
timer MUST be at least 30 minutes. The receipt of ANY command from
the client during that interval SHOULD suffice to reset the
autologout timer.
5.5. Multiple Commands in Progress
The client MAY send another command without waiting for the
completion result response of a command, subject to ambiguity rules
(see below) and flow control constraints on the underlying data
stream. Similarly, a server MAY begin processing another command
before processing the current command to completion, subject to
ambiguity rules. However, any command continuation request responses
and command continuations MUST be negotiated before any subsequent
command is initiated.
The exception is if an ambiguity would result because of a command
that would affect the results of other commands. Clients MUST NOT
send multiple commands without waiting if an ambiguity would result.
If the server detects a possible ambiguity, it MUST execute commands
to completion in the order given by the client.
The most obvious example of ambiguity is when a command would affect
the results of another command, e.g., a FETCH of a message's flags
and a STORE of that same message's flags.
A non-obvious ambiguity occurs with commands that permit an untagged
EXPUNGE response (commands other than FETCH, STORE, and SEARCH),
since an untagged EXPUNGE response can invalidate sequence numbers in
a subsequent command. This is not a problem for FETCH, STORE, or
SEARCH commands because servers are prohibited from sending EXPUNGE
responses while any of those commands are in progress. Therefore, if
the client sends any command other than FETCH, STORE, or SEARCH, it
MUST wait for the completion result response before sending a command
with message sequence numbers.
Note: UID FETCH, UID STORE, and UID SEARCH are different
commands from FETCH, STORE, and SEARCH. If the client
sends a UID command, it must wait for a completion result
response before sending a command with message sequence
numbers.
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For example, the following non-waiting command sequences are invalid:
FETCH + NOOP + STORE
STORE + COPY + FETCH
COPY + COPY
CHECK + FETCH
The following are examples of valid non-waiting command sequences:
FETCH + STORE + SEARCH + CHECK
STORE + COPY + EXPUNGE
UID SEARCH + UID SEARCH may be valid or invalid as a non-waiting
command sequence, depending upon whether or not the second UID
SEARCH contains message sequence numbers.
6. Client Commands
IMAP4rev1 commands are described in this section. Commands are
organized by the state in which the command is permitted. Commands
which are permitted in multiple states are listed in the minimum
permitted state (for example, commands valid in authenticated and
selected state are listed in the authenticated state commands).
Command arguments, identified by "Arguments:" in the command
descriptions below, are described by function, not by syntax. The
precise syntax of command arguments is described in the Formal Syntax
section.
Some commands cause specific server responses to be returned; these
are identified by "Responses:" in the command descriptions below.
See the response descriptions in the Responses section for
information on these responses, and the Formal Syntax section for the
precise syntax of these responses. It is possible for server data to
be transmitted as a result of any command. Thus, commands that do
not specifically require server data specify "no specific responses
for this command" instead of "none".
The "Result:" in the command description refers to the possible
tagged status responses to a command, and any special interpretation
of these status responses.
The state of a connection is only changed by successful commands
which are documented as changing state. A rejected command (BAD
response) never changes the state of the connection or of the
selected mailbox. A failed command (NO response) generally does not
change the state of the connection or of the selected mailbox; the
exception being the SELECT and EXAMINE commands.
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RFC 3501 IMAPv4 March 2003
6.1. Client Commands - Any State
The following commands are valid in any state: CAPABILITY, NOOP, and
LOGOUT.
6.1.1. CAPABILITY Command
Arguments: none
Responses: REQUIRED untagged response: CAPABILITY
Result: OK - capability completed
BAD - command unknown or arguments invalid
The CAPABILITY command requests a listing of capabilities that the
server supports. The server MUST send a single untagged
CAPABILITY response with "IMAP4rev1" as one of the listed
capabilities before the (tagged) OK response.
A capability name which begins with "AUTH=" indicates that the
server supports that particular authentication mechanism. All
such names are, by definition, part of this specification. For
example, the authorization capability for an experimental
"blurdybloop" authenticator would be "AUTH=XBLURDYBLOOP" and not
"XAUTH=BLURDYBLOOP" or "XAUTH=XBLURDYBLOOP".
Other capability names refer to extensions, revisions, or
amendments to this specification. See the documentation of the
CAPABILITY response for additional information. No capabilities,
beyond the base IMAP4rev1 set defined in this specification, are
enabled without explicit client action to invoke the capability.
Client and server implementations MUST implement the STARTTLS,
LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS])
capabilities. See the Security Considerations section for
important information.
See the section entitled "Client Commands -
Experimental/Expansion" for information about the form of site or
implementation-specific capabilities.
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6.1.3. LOGOUT Command
Arguments: none
Responses: REQUIRED untagged response: BYE
Result: OK - logout completed
BAD - command unknown or arguments invalid
The LOGOUT command informs the server that the client is done with
the connection. The server MUST send a BYE untagged response
before the (tagged) OK response, and then close the network
connection.
Example: C: A023 LOGOUT
S: * BYE IMAP4rev1 Server logging out
S: A023 OK LOGOUT completed
(Server and client then close the connection)
6.2. Client Commands - Not Authenticated State
In the not authenticated state, the AUTHENTICATE or LOGIN command
establishes authentication and enters the authenticated state. The
AUTHENTICATE command provides a general mechanism for a variety of
authentication techniques, privacy protection, and integrity
checking; whereas the LOGIN command uses a traditional user name and
plaintext password pair and has no means of establishing privacy
protection or integrity checking.
The STARTTLS command is an alternate form of establishing session
privacy protection and integrity checking, but does not establish
authentication or enter the authenticated state.
Server implementations MAY allow access to certain mailboxes without
establishing authentication. This can be done by means of the
ANONYMOUS [SASL] authenticator described in [ANONYMOUS]. An older
convention is a LOGIN command using the userid "anonymous"; in this
case, a password is required although the server may choose to accept
any password. The restrictions placed on anonymous users are
implementation-dependent.
Once authenticated (including as anonymous), it is not possible to
re-enter not authenticated state.
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In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the not authenticated state:
STARTTLS, AUTHENTICATE and LOGIN. See the Security Considerations
section for important information about these commands.
6.2.1. STARTTLS Command
Arguments: none
Responses: no specific response for this command
Result: OK - starttls completed, begin TLS negotiation
BAD - command unknown or arguments invalid
A [TLS] negotiation begins immediately after the CRLF at the end
of the tagged OK response from the server. Once a client issues a
STARTTLS command, it MUST NOT issue further commands until a
server response is seen and the [TLS] negotiation is complete.
The server remains in the non-authenticated state, even if client
credentials are supplied during the [TLS] negotiation. This does
not preclude an authentication mechanism such as EXTERNAL (defined
in [SASL]) from using client identity determined by the [TLS]
negotiation.
Once [TLS] has been started, the client MUST discard cached
information about server capabilities and SHOULD re-issue the
CAPABILITY command. This is necessary to protect against man-in-
the-middle attacks which alter the capabilities list prior to
STARTTLS. The server MAY advertise different capabilities after
STARTTLS.
Example: C: a001 CAPABILITY
S: * CAPABILITY IMAP4rev1 STARTTLS LOGINDISABLED
S: a001 OK CAPABILITY completed
C: a002 STARTTLS
S: a002 OK Begin TLS negotiation now
<TLS negotiation, further commands are under [TLS] layer>
C: a003 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=PLAIN
S: a003 OK CAPABILITY completed
C: a004 LOGIN joe password
S: a004 OK LOGIN completed
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6.2.2. AUTHENTICATE Command
Arguments: authentication mechanism name
Responses: continuation data can be requested
Result: OK - authenticate completed, now in authenticated state
NO - authenticate failure: unsupported authentication
mechanism, credentials rejected
BAD - command unknown or arguments invalid,
authentication exchange cancelled
The AUTHENTICATE command indicates a [SASL] authentication
mechanism to the server. If the server supports the requested
authentication mechanism, it performs an authentication protocol
exchange to authenticate and identify the client. It MAY also
negotiate an OPTIONAL security layer for subsequent protocol
interactions. If the requested authentication mechanism is not
supported, the server SHOULD reject the AUTHENTICATE command by
sending a tagged NO response.
The AUTHENTICATE command does not support the optional "initial
response" feature of [SASL]. Section 5.1 of [SASL] specifies how
to handle an authentication mechanism which uses an initial
response.
The service name specified by this protocol's profile of [SASL] is
"imap".
The authentication protocol exchange consists of a series of
server challenges and client responses that are specific to the
authentication mechanism. A server challenge consists of a
command continuation request response with the "+" token followed
by a BASE64 encoded string. The client response consists of a
single line consisting of a BASE64 encoded string. If the client
wishes to cancel an authentication exchange, it issues a line
consisting of a single "*". If the server receives such a
response, it MUST reject the AUTHENTICATE command by sending a
tagged BAD response.
If a security layer is negotiated through the [SASL]
authentication exchange, it takes effect immediately following the
CRLF that concludes the authentication exchange for the client,
and the CRLF of the tagged OK response for the server.
While client and server implementations MUST implement the
AUTHENTICATE command itself, it is not required to implement any
authentication mechanisms other than the PLAIN mechanism described
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RFC 3501 IMAPv4 March 2003
in [IMAP-TLS]. Also, an authentication mechanism is not required
to support any security layers.
Note: a server implementation MUST implement a
configuration in which it does NOT permit any plaintext
password mechanisms, unless either the STARTTLS command
has been negotiated or some other mechanism that
protects the session from password snooping has been
provided. Server sites SHOULD NOT use any configuration
which permits a plaintext password mechanism without
such a protection mechanism against password snooping.
Client and server implementations SHOULD implement
additional [SASL] mechanisms that do not use plaintext
passwords, such the GSSAPI mechanism described in [SASL]
and/or the [DIGEST-MD5] mechanism.
Servers and clients can support multiple authentication
mechanisms. The server SHOULD list its supported authentication
mechanisms in the response to the CAPABILITY command so that the
client knows which authentication mechanisms to use.
A server MAY include a CAPABILITY response code in the tagged OK
response of a successful AUTHENTICATE command in order to send
capabilities automatically. It is unnecessary for a client to
send a separate CAPABILITY command if it recognizes these
automatic capabilities. This should only be done if a security
layer was not negotiated by the AUTHENTICATE command, because the
tagged OK response as part of an AUTHENTICATE command is not
protected by encryption/integrity checking. [SASL] requires the
client to re-issue a CAPABILITY command in this case.
If an AUTHENTICATE command fails with a NO response, the client
MAY try another authentication mechanism by issuing another
AUTHENTICATE command. It MAY also attempt to authenticate by
using the LOGIN command (see section 6.2.3 for more detail). In
other words, the client MAY request authentication types in
decreasing order of preference, with the LOGIN command as a last
resort.
The authorization identity passed from the client to the server
during the authentication exchange is interpreted by the server as
the user name whose privileges the client is requesting.
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RFC 3501 IMAPv4 March 2003
A server MAY include a CAPABILITY response code in the tagged OK
response to a successful LOGIN command in order to send
capabilities automatically. It is unnecessary for a client to
send a separate CAPABILITY command if it recognizes these
automatic capabilities.
Example: C: a001 LOGIN SMITH SESAME
S: a001 OK LOGIN completed
Note: Use of the LOGIN command over an insecure network
(such as the Internet) is a security risk, because anyone
monitoring network traffic can obtain plaintext passwords.
The LOGIN command SHOULD NOT be used except as a last
resort, and it is recommended that client implementations
have a means to disable any automatic use of the LOGIN
command.
Unless either the STARTTLS command has been negotiated or
some other mechanism that protects the session from
password snooping has been provided, a server
implementation MUST implement a configuration in which it
advertises the LOGINDISABLED capability and does NOT permit
the LOGIN command. Server sites SHOULD NOT use any
configuration which permits the LOGIN command without such
a protection mechanism against password snooping. A client
implementation MUST NOT send a LOGIN command if the
LOGINDISABLED capability is advertised.
6.3. Client Commands - Authenticated State
In the authenticated state, commands that manipulate mailboxes as
atomic entities are permitted. Of these commands, the SELECT and
EXAMINE commands will select a mailbox for access and enter the
selected state.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
the following commands are valid in the authenticated state: SELECT,
EXAMINE, CREATE, DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB,
STATUS, and APPEND.
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RFC 3501 IMAPv4 March 2003
6.3.1. SELECT Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - select completed, now in selected state
NO - select failure, now in authenticated state: no
such mailbox, can't access mailbox
BAD - command unknown or arguments invalid
The SELECT command selects a mailbox so that messages in the
mailbox can be accessed. Before returning an OK to the client,
the server MUST send the following untagged data to the client.
Note that earlier versions of this protocol only required the
FLAGS, EXISTS, and RECENT untagged data; consequently, client
implementations SHOULD implement default behavior for missing data
as discussed with the individual item.
FLAGS Defined flags in the mailbox. See the description
of the FLAGS response for more detail.
<n> EXISTS The number of messages in the mailbox. See the
description of the EXISTS response for more detail.
<n> RECENT The number of messages with the \Recent flag set.
See the description of the RECENT response for more
detail.
OK [UNSEEN <n>]
The message sequence number of the first unseen
message in the mailbox. If this is missing, the
client can not make any assumptions about the first
unseen message in the mailbox, and needs to issue a
SEARCH command if it wants to find it.
OK [PERMANENTFLAGS (<list of flags>)]
A list of message flags that the client can change
permanently. If this is missing, the client should
assume that all flags can be changed permanently.
OK [UIDNEXT <n>]
The next unique identifier value. Refer to section
2.3.1.1 for more information. If this is missing,
the client can not make any assumptions about the
next unique identifier value.
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RFC 3501 IMAPv4 March 2003
OK [UIDVALIDITY <n>]
The unique identifier validity value. Refer to
section 2.3.1.1 for more information. If this is
missing, the server does not support unique
identifiers.
Only one mailbox can be selected at a time in a connection;
simultaneous access to multiple mailboxes requires multiple
connections. The SELECT command automatically deselects any
currently selected mailbox before attempting the new selection.
Consequently, if a mailbox is selected and a SELECT command that
fails is attempted, no mailbox is selected.
If the client is permitted to modify the mailbox, the server
SHOULD prefix the text of the tagged OK response with the
"[READ-WRITE]" response code.
If the client is not permitted to modify the mailbox but is
permitted read access, the mailbox is selected as read-only, and
the server MUST prefix the text of the tagged OK response to
SELECT with the "[READ-ONLY]" response code. Read-only access
through SELECT differs from the EXAMINE command in that certain
read-only mailboxes MAY permit the change of permanent state on a
per-user (as opposed to global) basis. Netnews messages marked in
a server-based .newsrc file are an example of such per-user
permanent state that can be modified with read-only mailboxes.
Example: C: A142 SELECT INBOX
S: * 172 EXISTS
S: * 1 RECENT
S: * OK [UNSEEN 12] Message 12 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
S: A142 OK [READ-WRITE] SELECT completed
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RFC 3501 IMAPv4 March 2003
6.3.2. EXAMINE Command
Arguments: mailbox name
Responses: REQUIRED untagged responses: FLAGS, EXISTS, RECENT
REQUIRED OK untagged responses: UNSEEN, PERMANENTFLAGS,
UIDNEXT, UIDVALIDITY
Result: OK - examine completed, now in selected state
NO - examine failure, now in authenticated state: no
such mailbox, can't access mailbox
BAD - command unknown or arguments invalid
The EXAMINE command is identical to SELECT and returns the same
output; however, the selected mailbox is identified as read-only.
No changes to the permanent state of the mailbox, including
per-user state, are permitted; in particular, EXAMINE MUST NOT
cause messages to lose the \Recent flag.
The text of the tagged OK response to the EXAMINE command MUST
begin with the "[READ-ONLY]" response code.
Example: C: A932 EXAMINE blurdybloop
S: * 17 EXISTS
S: * 2 RECENT
S: * OK [UNSEEN 8] Message 8 is first unseen
S: * OK [UIDVALIDITY 3857529045] UIDs valid
S: * OK [UIDNEXT 4392] Predicted next UID
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()] No permanent flags permitted
S: A932 OK [READ-ONLY] EXAMINE completed
6.3.3. CREATE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - create completed
NO - create failure: can't create mailbox with that name
BAD - command unknown or arguments invalid
The CREATE command creates a mailbox with the given name. An OK
response is returned only if a new mailbox with that name has been
created. It is an error to attempt to create INBOX or a mailbox
with a name that refers to an extant mailbox. Any error in
creation will return a tagged NO response.
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RFC 3501 IMAPv4 March 2003
If the mailbox name is suffixed with the server's hierarchy
separator character (as returned from the server by a LIST
command), this is a declaration that the client intends to create
mailbox names under this name in the hierarchy. Server
implementations that do not require this declaration MUST ignore
the declaration. In any case, the name created is without the
trailing hierarchy delimiter.
If the server's hierarchy separator character appears elsewhere in
the name, the server SHOULD create any superior hierarchical names
that are needed for the CREATE command to be successfully
completed. In other words, an attempt to create "foo/bar/zap" on
a server in which "/" is the hierarchy separator character SHOULD
create foo/ and foo/bar/ if they do not already exist.
If a new mailbox is created with the same name as a mailbox which
was deleted, its unique identifiers MUST be greater than any
unique identifiers used in the previous incarnation of the mailbox
UNLESS the new incarnation has a different unique identifier
validity value. See the description of the UID command for more
detail.
Example: C: A003 CREATE owatagusiam/
S: A003 OK CREATE completed
C: A004 CREATE owatagusiam/blurdybloop
S: A004 OK CREATE completed
Note: The interpretation of this example depends on whether
"/" was returned as the hierarchy separator from LIST. If
"/" is the hierarchy separator, a new level of hierarchy
named "owatagusiam" with a member called "blurdybloop" is
created. Otherwise, two mailboxes at the same hierarchy
level are created.
6.3.4. DELETE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - delete completed
NO - delete failure: can't delete mailbox with that name
BAD - command unknown or arguments invalid
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RFC 3501 IMAPv4 March 2003
The DELETE command permanently removes the mailbox with the given
name. A tagged OK response is returned only if the mailbox has
been deleted. It is an error to attempt to delete INBOX or a
mailbox name that does not exist.
The DELETE command MUST NOT remove inferior hierarchical names.
For example, if a mailbox "foo" has an inferior "foo.bar"
(assuming "." is the hierarchy delimiter character), removing
"foo" MUST NOT remove "foo.bar". It is an error to attempt to
delete a name that has inferior hierarchical names and also has
the \Noselect mailbox name attribute (see the description of the
LIST response for more details).
It is permitted to delete a name that has inferior hierarchical
names and does not have the \Noselect mailbox name attribute. In
this case, all messages in that mailbox are removed, and the name
will acquire the \Noselect mailbox name attribute.
The value of the highest-used unique identifier of the deleted
mailbox MUST be preserved so that a new mailbox created with the
same name will not reuse the identifiers of the former
incarnation, UNLESS the new incarnation has a different unique
identifier validity value. See the description of the UID command
for more detail.
Examples: C: A682 LIST "" *
S: * LIST () "/" blurdybloop
S: * LIST (\Noselect) "/" foo
S: * LIST () "/" foo/bar
S: A682 OK LIST completed
C: A683 DELETE blurdybloop
S: A683 OK DELETE completed
C: A684 DELETE foo
S: A684 NO Name "foo" has inferior hierarchical names
C: A685 DELETE foo/bar
S: A685 OK DELETE Completed
C: A686 LIST "" *
S: * LIST (\Noselect) "/" foo
S: A686 OK LIST completed
C: A687 DELETE foo
S: A687 OK DELETE Completed
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RFC 3501 IMAPv4 March 2003
C: A82 LIST "" *
S: * LIST () "." blurdybloop
S: * LIST () "." foo
S: * LIST () "." foo.bar
S: A82 OK LIST completed
C: A83 DELETE blurdybloop
S: A83 OK DELETE completed
C: A84 DELETE foo
S: A84 OK DELETE Completed
C: A85 LIST "" *
S: * LIST () "." foo.bar
S: A85 OK LIST completed
C: A86 LIST "" %
S: * LIST (\Noselect) "." foo
S: A86 OK LIST completed
6.3.5. RENAME Command
Arguments: existing mailbox name
new mailbox name
Responses: no specific responses for this command
Result: OK - rename completed
NO - rename failure: can't rename mailbox with that name,
can't rename to mailbox with that name
BAD - command unknown or arguments invalid
The RENAME command changes the name of a mailbox. A tagged OK
response is returned only if the mailbox has been renamed. It is
an error to attempt to rename from a mailbox name that does not
exist or to a mailbox name that already exists. Any error in
renaming will return a tagged NO response.
If the name has inferior hierarchical names, then the inferior
hierarchical names MUST also be renamed. For example, a rename of
"foo" to "zap" will rename "foo/bar" (assuming "/" is the
hierarchy delimiter character) to "zap/bar".
If the server's hierarchy separator character appears in the name,
the server SHOULD create any superior hierarchical names that are
needed for the RENAME command to complete successfully. In other
words, an attempt to rename "foo/bar/zap" to baz/rag/zowie on a
server in which "/" is the hierarchy separator character SHOULD
create baz/ and baz/rag/ if they do not already exist.
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RFC 3501 IMAPv4 March 2003
6.3.6. SUBSCRIBE Command
Arguments: mailbox
Responses: no specific responses for this command
Result: OK - subscribe completed
NO - subscribe failure: can't subscribe to that name
BAD - command unknown or arguments invalid
The SUBSCRIBE command adds the specified mailbox name to the
server's set of "active" or "subscribed" mailboxes as returned by
the LSUB command. This command returns a tagged OK response only
if the subscription is successful.
A server MAY validate the mailbox argument to SUBSCRIBE to verify
that it exists. However, it MUST NOT unilaterally remove an
existing mailbox name from the subscription list even if a mailbox
by that name no longer exists.
Note: This requirement is because a server site can
choose to routinely remove a mailbox with a well-known
name (e.g., "system-alerts") after its contents expire,
with the intention of recreating it when new contents
are appropriate.
Example: C: A002 SUBSCRIBE #news.comp.mail.mime
S: A002 OK SUBSCRIBE completed
6.3.7. UNSUBSCRIBE Command
Arguments: mailbox name
Responses: no specific responses for this command
Result: OK - unsubscribe completed
NO - unsubscribe failure: can't unsubscribe that name
BAD - command unknown or arguments invalid
The UNSUBSCRIBE command removes the specified mailbox name from
the server's set of "active" or "subscribed" mailboxes as returned
by the LSUB command. This command returns a tagged OK response
only if the unsubscription is successful.
Example: C: A002 UNSUBSCRIBE #news.comp.mail.mime
S: A002 OK UNSUBSCRIBE completed
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6.3.8. LIST Command
Arguments: reference name
mailbox name with possible wildcards
Responses: untagged responses: LIST
Result: OK - list completed
NO - list failure: can't list that reference or name
BAD - command unknown or arguments invalid
The LIST command returns a subset of names from the complete set
of all names available to the client. Zero or more untagged LIST
replies are returned, containing the name attributes, hierarchy
delimiter, and name; see the description of the LIST reply for
more detail.
The LIST command SHOULD return its data quickly, without undue
delay. For example, it SHOULD NOT go to excess trouble to
calculate the \Marked or \Unmarked status or perform other
processing; if each name requires 1 second of processing, then a
list of 1200 names would take 20 minutes!
An empty ("" string) reference name argument indicates that the
mailbox name is interpreted as by SELECT. The returned mailbox
names MUST match the supplied mailbox name pattern. A non-empty
reference name argument is the name of a mailbox or a level of
mailbox hierarchy, and indicates the context in which the mailbox
name is interpreted.
An empty ("" string) mailbox name argument is a special request to
return the hierarchy delimiter and the root name of the name given
in the reference. The value returned as the root MAY be the empty
string if the reference is non-rooted or is an empty string. In
all cases, a hierarchy delimiter (or NIL if there is no hierarchy)
is returned. This permits a client to get the hierarchy delimiter
(or find out that the mailbox names are flat) even when no
mailboxes by that name currently exist.
The reference and mailbox name arguments are interpreted into a
canonical form that represents an unambiguous left-to-right
hierarchy. The returned mailbox names will be in the interpreted
form.
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Note: The interpretation of the reference argument is
implementation-defined. It depends upon whether the
server implementation has a concept of the "current
working directory" and leading "break out characters",
which override the current working directory.
For example, on a server which exports a UNIX or NT
filesystem, the reference argument contains the current
working directory, and the mailbox name argument would
contain the name as interpreted in the current working
directory.
If a server implementation has no concept of break out
characters, the canonical form is normally the reference
name appended with the mailbox name. Note that if the
server implements the namespace convention (section
5.1.2), "#" is a break out character and must be treated
as such.
If the reference argument is not a level of mailbox
hierarchy (that is, it is a \NoInferiors name), and/or
the reference argument does not end with the hierarchy
delimiter, it is implementation-dependent how this is
interpreted. For example, a reference of "foo/bar" and
mailbox name of "rag/baz" could be interpreted as
"foo/bar/rag/baz", "foo/barrag/baz", or "foo/rag/baz".
A client SHOULD NOT use such a reference argument except
at the explicit request of the user. A hierarchical
browser MUST NOT make any assumptions about server
interpretation of the reference unless the reference is
a level of mailbox hierarchy AND ends with the hierarchy
delimiter.
Any part of the reference argument that is included in the
interpreted form SHOULD prefix the interpreted form. It SHOULD
also be in the same form as the reference name argument. This
rule permits the client to determine if the returned mailbox name
is in the context of the reference argument, or if something about
the mailbox argument overrode the reference argument. Without
this rule, the client would have to have knowledge of the server's
naming semantics including what characters are "breakouts" that
override a naming context.
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For example, here are some examples of how references
and mailbox names might be interpreted on a UNIX-based
server:
Reference Mailbox Name Interpretation
------------ ------------ --------------
~smith/Mail/ foo.* ~smith/Mail/foo.*
archive/ % archive/%
#news. comp.mail.* #news.comp.mail.*
~smith/Mail/ /usr/doc/foo /usr/doc/foo
archive/ ~fred/Mail/* ~fred/Mail/*
The first three examples demonstrate interpretations in
the context of the reference argument. Note that
"~smith/Mail" SHOULD NOT be transformed into something
like "/u2/users/smith/Mail", or it would be impossible
for the client to determine that the interpretation was
in the context of the reference.
The character "*" is a wildcard, and matches zero or more
characters at this position. The character "%" is similar to "*",
but it does not match a hierarchy delimiter. If the "%" wildcard
is the last character of a mailbox name argument, matching levels
of hierarchy are also returned. If these levels of hierarchy are
not also selectable mailboxes, they are returned with the
\Noselect mailbox name attribute (see the description of the LIST
response for more details).
Server implementations are permitted to "hide" otherwise
accessible mailboxes from the wildcard characters, by preventing
certain characters or names from matching a wildcard in certain
situations. For example, a UNIX-based server might restrict the
interpretation of "*" so that an initial "/" character does not
match.
The special name INBOX is included in the output from LIST, if
INBOX is supported by this server for this user and if the
uppercase string "INBOX" matches the interpreted reference and
mailbox name arguments with wildcards as described above. The
criteria for omitting INBOX is whether SELECT INBOX will return
failure; it is not relevant whether the user's real INBOX resides
on this or some other server.
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Example: C: A101 LIST "" ""
S: * LIST (\Noselect) "/" ""
S: A101 OK LIST Completed
C: A102 LIST #news.comp.mail.misc ""
S: * LIST (\Noselect) "." #news.
S: A102 OK LIST Completed
C: A103 LIST /usr/staff/jones ""
S: * LIST (\Noselect) "/" /
S: A103 OK LIST Completed
C: A202 LIST ~/Mail/ %
S: * LIST (\Noselect) "/" ~/Mail/foo
S: * LIST () "/" ~/Mail/meetings
S: A202 OK LIST completed
6.3.9. LSUB Command
Arguments: reference name
mailbox name with possible wildcards
Responses: untagged responses: LSUB
Result: OK - lsub completed
NO - lsub failure: can't list that reference or name
BAD - command unknown or arguments invalid
The LSUB command returns a subset of names from the set of names
that the user has declared as being "active" or "subscribed".
Zero or more untagged LSUB replies are returned. The arguments to
LSUB are in the same form as those for LIST.
The returned untagged LSUB response MAY contain different mailbox
flags from a LIST untagged response. If this should happen, the
flags in the untagged LIST are considered more authoritative.
A special situation occurs when using LSUB with the % wildcard.
Consider what happens if "foo/bar" (with a hierarchy delimiter of
"/") is subscribed but "foo" is not. A "%" wildcard to LSUB must
return foo, not foo/bar, in the LSUB response, and it MUST be
flagged with the \Noselect attribute.
The server MUST NOT unilaterally remove an existing mailbox name
from the subscription list even if a mailbox by that name no
longer exists.
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Example: C: A002 LSUB "#news." "comp.mail.*"
S: * LSUB () "." #news.comp.mail.mime
S: * LSUB () "." #news.comp.mail.misc
S: A002 OK LSUB completed
C: A003 LSUB "#news." "comp.%"
S: * LSUB (\NoSelect) "." #news.comp.mail
S: A003 OK LSUB completed
6.3.10. STATUS Command
Arguments: mailbox name
status data item names
Responses: untagged responses: STATUS
Result: OK - status completed
NO - status failure: no status for that name
BAD - command unknown or arguments invalid
The STATUS command requests the status of the indicated mailbox.
It does not change the currently selected mailbox, nor does it
affect the state of any messages in the queried mailbox (in
particular, STATUS MUST NOT cause messages to lose the \Recent
flag).
The STATUS command provides an alternative to opening a second
IMAP4rev1 connection and doing an EXAMINE command on a mailbox to
query that mailbox's status without deselecting the current
mailbox in the first IMAP4rev1 connection.
Unlike the LIST command, the STATUS command is not guaranteed to
be fast in its response. Under certain circumstances, it can be
quite slow. In some implementations, the server is obliged to
open the mailbox read-only internally to obtain certain status
information. Also unlike the LIST command, the STATUS command
does not accept wildcards.
Note: The STATUS command is intended to access the
status of mailboxes other than the currently selected
mailbox. Because the STATUS command can cause the
mailbox to be opened internally, and because this
information is available by other means on the selected
mailbox, the STATUS command SHOULD NOT be used on the
currently selected mailbox.
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The STATUS command MUST NOT be used as a "check for new
messages in the selected mailbox" operation (refer to
sections 7, 7.3.1, and 7.3.2 for more information about
the proper method for new message checking).
Because the STATUS command is not guaranteed to be fast
in its results, clients SHOULD NOT expect to be able to
issue many consecutive STATUS commands and obtain
reasonable performance.
The currently defined status data items that can be requested are:
MESSAGES
The number of messages in the mailbox.
RECENT
The number of messages with the \Recent flag set.
UIDNEXT
The next unique identifier value of the mailbox. Refer to
section 2.3.1.1 for more information.
UIDVALIDITY
The unique identifier validity value of the mailbox. Refer to
section 2.3.1.1 for more information.
UNSEEN
The number of messages which do not have the \Seen flag set.
Example: C: A042 STATUS blurdybloop (UIDNEXT MESSAGES)
S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
S: A042 OK STATUS completed
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6.3.11. APPEND Command
Arguments: mailbox name
OPTIONAL flag parenthesized list
OPTIONAL date/time string
message literal
Responses: no specific responses for this command
Result: OK - append completed
NO - append error: can't append to that mailbox, error
in flags or date/time or message text
BAD - command unknown or arguments invalid
The APPEND command appends the literal argument as a new message
to the end of the specified destination mailbox. This argument
SHOULD be in the format of an [RFC-2822] message. 8-bit
characters are permitted in the message. A server implementation
that is unable to preserve 8-bit data properly MUST be able to
reversibly convert 8-bit APPEND data to 7-bit using a [MIME-IMB]
content transfer encoding.
Note: There MAY be exceptions, e.g., draft messages, in
which required [RFC-2822] header lines are omitted in
the message literal argument to APPEND. The full
implications of doing so MUST be understood and
carefully weighed.
If a flag parenthesized list is specified, the flags SHOULD be set
in the resulting message; otherwise, the flag list of the
resulting message is set to empty by default. In either case, the
Recent flag is also set.
If a date-time is specified, the internal date SHOULD be set in
the resulting message; otherwise, the internal date of the
resulting message is set to the current date and time by default.
If the append is unsuccessful for any reason, the mailbox MUST be
restored to its state before the APPEND attempt; no partial
appending is permitted.
If the destination mailbox does not exist, a server MUST return an
error, and MUST NOT automatically create the mailbox. Unless it
is certain that the destination mailbox can not be created, the
server MUST send the response code "[TRYCREATE]" as the prefix of
the text of the tagged NO response. This gives a hint to the
client that it can attempt a CREATE command and retry the APPEND
if the CREATE is successful.
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If the mailbox is currently selected, the normal new message
actions SHOULD occur. Specifically, the server SHOULD notify the
client immediately via an untagged EXISTS response. If the server
does not do so, the client MAY issue a NOOP command (or failing
that, a CHECK command) after one or more APPEND commands.
Example: C: A003 APPEND saved-messages (\Seen) {310}
S: + Ready for literal data
C: Date: Mon, 7 Feb 1994 21:52:25 -0800 (PST)
C: From: Fred Foobar <foobar@Blurdybloop.COM>
C: Subject: afternoon meeting
C: To: mooch@owatagu.siam.edu
C: Message-Id: <B27397-0100000@Blurdybloop.COM>
C: MIME-Version: 1.0
C: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
C:
C: Hello Joe, do you think we can meet at 3:30 tomorrow?
C:
S: A003 OK APPEND completed
Note: The APPEND command is not used for message delivery,
because it does not provide a mechanism to transfer [SMTP]
envelope information.
6.4. Client Commands - Selected State
In the selected state, commands that manipulate messages in a mailbox
are permitted.
In addition to the universal commands (CAPABILITY, NOOP, and LOGOUT),
and the authenticated state commands (SELECT, EXAMINE, CREATE,
DELETE, RENAME, SUBSCRIBE, UNSUBSCRIBE, LIST, LSUB, STATUS, and
APPEND), the following commands are valid in the selected state:
CHECK, CLOSE, EXPUNGE, SEARCH, FETCH, STORE, COPY, and UID.
6.4.1. CHECK Command
Arguments: none
Responses: no specific responses for this command
Result: OK - check completed
BAD - command unknown or arguments invalid
The CHECK command requests a checkpoint of the currently selected
mailbox. A checkpoint refers to any implementation-dependent
housekeeping associated with the mailbox (e.g., resolving the
server's in-memory state of the mailbox with the state on its
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RFC 3501 IMAPv4 March 2003
disk) that is not normally executed as part of each command. A
checkpoint MAY take a non-instantaneous amount of real time to
complete. If a server implementation has no such housekeeping
considerations, CHECK is equivalent to NOOP.
There is no guarantee that an EXISTS untagged response will happen
as a result of CHECK. NOOP, not CHECK, SHOULD be used for new
message polling.
Example: C: FXXZ CHECK
S: FXXZ OK CHECK Completed
6.4.2. CLOSE Command
Arguments: none
Responses: no specific responses for this command
Result: OK - close completed, now in authenticated state
BAD - command unknown or arguments invalid
The CLOSE command permanently removes all messages that have the
\Deleted flag set from the currently selected mailbox, and returns
to the authenticated state from the selected state. No untagged
EXPUNGE responses are sent.
No messages are removed, and no error is given, if the mailbox is
selected by an EXAMINE command or is otherwise selected read-only.
Even if a mailbox is selected, a SELECT, EXAMINE, or LOGOUT
command MAY be issued without previously issuing a CLOSE command.
The SELECT, EXAMINE, and LOGOUT commands implicitly close the
currently selected mailbox without doing an expunge. However,
when many messages are deleted, a CLOSE-LOGOUT or CLOSE-SELECT
sequence is considerably faster than an EXPUNGE-LOGOUT or
EXPUNGE-SELECT because no untagged EXPUNGE responses (which the
client would probably ignore) are sent.
Example: C: A341 CLOSE
S: A341 OK CLOSE completed
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When multiple keys are specified, the result is the intersection
(AND function) of all the messages that match those keys. For
example, the criteria DELETED FROM "SMITH" SINCE 1-Feb-1994 refers
to all deleted messages from Smith that were placed in the mailbox
since February 1, 1994. A search key can also be a parenthesized
list of one or more search keys (e.g., for use with the OR and NOT
keys).
Server implementations MAY exclude [MIME-IMB] body parts with
terminal content media types other than TEXT and MESSAGE from
consideration in SEARCH matching.
The OPTIONAL [CHARSET] specification consists of the word
"CHARSET" followed by a registered [CHARSET]. It indicates the
[CHARSET] of the strings that appear in the search criteria.
[MIME-IMB] content transfer encodings, and [MIME-HDRS] strings in
[RFC-2822]/[MIME-IMB] headers, MUST be decoded before comparing
text in a [CHARSET] other than US-ASCII. US-ASCII MUST be
supported; other [CHARSET]s MAY be supported.
If the server does not support the specified [CHARSET], it MUST
return a tagged NO response (not a BAD). This response SHOULD
contain the BADCHARSET response code, which MAY list the
[CHARSET]s supported by the server.
In all search keys that use strings, a message matches the key if
the string is a substring of the field. The matching is
case-insensitive.
The defined search keys are as follows. Refer to the Formal
Syntax section for the precise syntactic definitions of the
arguments.
<sequence set>
Messages with message sequence numbers corresponding to the
specified message sequence number set.
ALL
All messages in the mailbox; the default initial key for
ANDing.
ANSWERED
Messages with the \Answered flag set.
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RFC 3501 IMAPv4 March 2003
BCC <string>
Messages that contain the specified string in the envelope
structure's BCC field.
BEFORE <date>
Messages whose internal date (disregarding time and timezone)
is earlier than the specified date.
BODY <string>
Messages that contain the specified string in the body of the
message.
CC <string>
Messages that contain the specified string in the envelope
structure's CC field.
DELETED
Messages with the \Deleted flag set.
DRAFT
Messages with the \Draft flag set.
FLAGGED
Messages with the \Flagged flag set.
FROM <string>
Messages that contain the specified string in the envelope
structure's FROM field.
HEADER <field-name> <string>
Messages that have a header with the specified field-name (as
defined in [RFC-2822]) and that contains the specified string
in the text of the header (what comes after the colon). If the
string to search is zero-length, this matches all messages that
have a header line with the specified field-name regardless of
the contents.
KEYWORD <flag>
Messages with the specified keyword flag set.
LARGER <n>
Messages with an [RFC-2822] size larger than the specified
number of octets.
NEW
Messages that have the \Recent flag set but not the \Seen flag.
This is functionally equivalent to "(RECENT UNSEEN)".
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RFC 3501 IMAPv4 March 2003
NOT <search-key>
Messages that do not match the specified search key.
OLD
Messages that do not have the \Recent flag set. This is
functionally equivalent to "NOT RECENT" (as opposed to "NOT
NEW").
ON <date>
Messages whose internal date (disregarding time and timezone)
is within the specified date.
OR <search-key1> <search-key2>
Messages that match either search key.
RECENT
Messages that have the \Recent flag set.
SEEN
Messages that have the \Seen flag set.
SENTBEFORE <date>
Messages whose [RFC-2822] Date: header (disregarding time and
timezone) is earlier than the specified date.
SENTON <date>
Messages whose [RFC-2822] Date: header (disregarding time and
timezone) is within the specified date.
SENTSINCE <date>
Messages whose [RFC-2822] Date: header (disregarding time and
timezone) is within or later than the specified date.
SINCE <date>
Messages whose internal date (disregarding time and timezone)
is within or later than the specified date.
SMALLER <n>
Messages with an [RFC-2822] size smaller than the specified
number of octets.
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RFC 3501 IMAPv4 March 2003
SUBJECT <string>
Messages that contain the specified string in the envelope
structure's SUBJECT field.
TEXT <string>
Messages that contain the specified string in the header or
body of the message.
TO <string>
Messages that contain the specified string in the envelope
structure's TO field.
UID <sequence set>
Messages with unique identifiers corresponding to the specified
unique identifier set. Sequence set ranges are permitted.
UNANSWERED
Messages that do not have the \Answered flag set.
UNDELETED
Messages that do not have the \Deleted flag set.
UNDRAFT
Messages that do not have the \Draft flag set.
UNFLAGGED
Messages that do not have the \Flagged flag set.
UNKEYWORD <flag>
Messages that do not have the specified keyword flag set.
UNSEEN
Messages that do not have the \Seen flag set.
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RFC 3501 IMAPv4 March 2003
Example: C: A282 SEARCH FLAGGED SINCE 1-Feb-1994 NOT FROM "Smith"
S: * SEARCH 2 84 882
S: A282 OK SEARCH completed
C: A283 SEARCH TEXT "string not in mailbox"
S: * SEARCH
S: A283 OK SEARCH completed
C: A284 SEARCH CHARSET UTF-8 TEXT {6}
C: XXXXXX
S: * SEARCH 43
S: A284 OK SEARCH completed
Note: Since this document is restricted to 7-bit ASCII
text, it is not possible to show actual UTF-8 data. The
"XXXXXX" is a placeholder for what would be 6 octets of
8-bit data in an actual transaction.
6.4.5. FETCH Command
Arguments: sequence set
message data item names or macro
Responses: untagged responses: FETCH
Result: OK - fetch completed
NO - fetch error: can't fetch that data
BAD - command unknown or arguments invalid
The FETCH command retrieves data associated with a message in the
mailbox. The data items to be fetched can be either a single atom
or a parenthesized list.
Most data items, identified in the formal syntax under the
msg-att-static rule, are static and MUST NOT change for any
particular message. Other data items, identified in the formal
syntax under the msg-att-dynamic rule, MAY change, either as a
result of a STORE command or due to external events.
For example, if a client receives an ENVELOPE for a
message when it already knows the envelope, it can
safely ignore the newly transmitted envelope.
There are three macros which specify commonly-used sets of data
items, and can be used instead of data items. A macro must be
used by itself, and not in conjunction with other macros or data
items.
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RFC 3501 IMAPv4 March 2003
ALL
Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE)
FAST
Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE)
FULL
Macro equivalent to: (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE
BODY)
The currently defined data items that can be fetched are:
BODY
Non-extensible form of BODYSTRUCTURE.
BODY[<section>]<<partial>>
The text of a particular body section. The section
specification is a set of zero or more part specifiers
delimited by periods. A part specifier is either a part number
or one of the following: HEADER, HEADER.FIELDS,
HEADER.FIELDS.NOT, MIME, and TEXT. An empty section
specification refers to the entire message, including the
header.
Every message has at least one part number. Non-[MIME-IMB]
messages, and non-multipart [MIME-IMB] messages with no
encapsulated message, only have a part 1.
Multipart messages are assigned consecutive part numbers, as
they occur in the message. If a particular part is of type
message or multipart, its parts MUST be indicated by a period
followed by the part number within that nested multipart part.
A part of type MESSAGE/RFC822 also has nested part numbers,
referring to parts of the MESSAGE part's body.
The HEADER, HEADER.FIELDS, HEADER.FIELDS.NOT, and TEXT part
specifiers can be the sole part specifier or can be prefixed by
one or more numeric part specifiers, provided that the numeric
part specifier refers to a part of type MESSAGE/RFC822. The
MIME part specifier MUST be prefixed by one or more numeric
part specifiers.
The HEADER, HEADER.FIELDS, and HEADER.FIELDS.NOT part
specifiers refer to the [RFC-2822] header of the message or of
an encapsulated [MIME-IMT] MESSAGE/RFC822 message.
HEADER.FIELDS and HEADER.FIELDS.NOT are followed by a list of
field-name (as defined in [RFC-2822]) names, and return a
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RFC 3501 IMAPv4 March 2003
subset of the header. The subset returned by HEADER.FIELDS
contains only those header fields with a field-name that
matches one of the names in the list; similarly, the subset
returned by HEADER.FIELDS.NOT contains only the header fields
with a non-matching field-name. The field-matching is
case-insensitive but otherwise exact. Subsetting does not
exclude the [RFC-2822] delimiting blank line between the header
and the body; the blank line is included in all header fetches,
except in the case of a message which has no body and no blank
line.
The MIME part specifier refers to the [MIME-IMB] header for
this part.
The TEXT part specifier refers to the text body of the message,
omitting the [RFC-2822] header.
Here is an example of a complex message with some of its
part specifiers:
HEADER ([RFC-2822] header of the message)
TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
1 TEXT/PLAIN
2 APPLICATION/OCTET-STREAM
3 MESSAGE/RFC822
3.HEADER ([RFC-2822] header of the message)
3.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
3.1 TEXT/PLAIN
3.2 APPLICATION/OCTET-STREAM
4 MULTIPART/MIXED
4.1 IMAGE/GIF
4.1.MIME ([MIME-IMB] header for the IMAGE/GIF)
4.2 MESSAGE/RFC822
4.2.HEADER ([RFC-2822] header of the message)
4.2.TEXT ([RFC-2822] text body of the message) MULTIPART/MIXED
4.2.1 TEXT/PLAIN
4.2.2 MULTIPART/ALTERNATIVE
4.2.2.1 TEXT/PLAIN
4.2.2.2 TEXT/RICHTEXT
It is possible to fetch a substring of the designated text.
This is done by appending an open angle bracket ("<"), the
octet position of the first desired octet, a period, the
maximum number of octets desired, and a close angle bracket
(">") to the part specifier. If the starting octet is beyond
the end of the text, an empty string is returned.
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RFC 3501 IMAPv4 March 2003
Any partial fetch that attempts to read beyond the end of the
text is truncated as appropriate. A partial fetch that starts
at octet 0 is returned as a partial fetch, even if this
truncation happened.
Note: This means that BODY[]<0.2048> of a 1500-octet message
will return BODY[]<0> with a literal of size 1500, not
BODY[].
Note: A substring fetch of a HEADER.FIELDS or
HEADER.FIELDS.NOT part specifier is calculated after
subsetting the header.
The \Seen flag is implicitly set; if this causes the flags to
change, they SHOULD be included as part of the FETCH responses.
BODY.PEEK[<section>]<<partial>>
An alternate form of BODY[<section>] that does not implicitly
set the \Seen flag.
BODYSTRUCTURE
The [MIME-IMB] body structure of the message. This is computed
by the server by parsing the [MIME-IMB] header fields in the
[RFC-2822] header and [MIME-IMB] headers.
ENVELOPE
The envelope structure of the message. This is computed by the
server by parsing the [RFC-2822] header into the component
parts, defaulting various fields as necessary.
FLAGS
The flags that are set for this message.
INTERNALDATE
The internal date of the message.
RFC822
Functionally equivalent to BODY[], differing in the syntax of
the resulting untagged FETCH data (RFC822 is returned).
RFC822.HEADER
Functionally equivalent to BODY.PEEK[HEADER], differing in the
syntax of the resulting untagged FETCH data (RFC822.HEADER is
returned).
RFC822.SIZE
The [RFC-2822] size of the message.
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RFC822.TEXT
Functionally equivalent to BODY[TEXT], differing in the syntax
of the resulting untagged FETCH data (RFC822.TEXT is returned).
UID
The unique identifier for the message.
Example: C: A654 FETCH 2:4 (FLAGS BODY[HEADER.FIELDS (DATE FROM)])
S: * 2 FETCH ....
S: * 3 FETCH ....
S: * 4 FETCH ....
S: A654 OK FETCH completed
6.4.6. STORE Command
Arguments: sequence set
message data item name
value for message data item
Responses: untagged responses: FETCH
Result: OK - store completed
NO - store error: can't store that data
BAD - command unknown or arguments invalid
The STORE command alters data associated with a message in the
mailbox. Normally, STORE will return the updated value of the
data with an untagged FETCH response. A suffix of ".SILENT" in
the data item name prevents the untagged FETCH, and the server
SHOULD assume that the client has determined the updated value
itself or does not care about the updated value.
Note: Regardless of whether or not the ".SILENT" suffix
was used, the server SHOULD send an untagged FETCH
response if a change to a message's flags from an
external source is observed. The intent is that the
status of the flags is determinate without a race
condition.
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The currently defined data items that can be stored are:
FLAGS <flag list>
Replace the flags for the message (other than \Recent) with the
argument. The new value of the flags is returned as if a FETCH
of those flags was done.
FLAGS.SILENT <flag list>
Equivalent to FLAGS, but without returning a new value.
+FLAGS <flag list>
Add the argument to the flags for the message. The new value
of the flags is returned as if a FETCH of those flags was done.
+FLAGS.SILENT <flag list>
Equivalent to +FLAGS, but without returning a new value.
-FLAGS <flag list>
Remove the argument from the flags for the message. The new
value of the flags is returned as if a FETCH of those flags was
done.
-FLAGS.SILENT <flag list>
Equivalent to -FLAGS, but without returning a new value.
Example: C: A003 STORE 2:4 +FLAGS (\Deleted)
S: * 2 FETCH (FLAGS (\Deleted \Seen))
S: * 3 FETCH (FLAGS (\Deleted))
S: * 4 FETCH (FLAGS (\Deleted \Flagged \Seen))
S: A003 OK STORE completed
6.4.7. COPY Command
Arguments: sequence set
mailbox name
Responses: no specific responses for this command
Result: OK - copy completed
NO - copy error: can't copy those messages or to that
name
BAD - command unknown or arguments invalid
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The COPY command copies the specified message(s) to the end of the
specified destination mailbox. The flags and internal date of the
message(s) SHOULD be preserved, and the Recent flag SHOULD be set,
in the copy.
If the destination mailbox does not exist, a server SHOULD return
an error. It SHOULD NOT automatically create the mailbox. Unless
it is certain that the destination mailbox can not be created, the
server MUST send the response code "[TRYCREATE]" as the prefix of
the text of the tagged NO response. This gives a hint to the
client that it can attempt a CREATE command and retry the COPY if
the CREATE is successful.
If the COPY command is unsuccessful for any reason, server
implementations MUST restore the destination mailbox to its state
before the COPY attempt.
Example: C: A003 COPY 2:4 MEETING
S: A003 OK COPY completed
6.4.8. UID Command
Arguments: command name
command arguments
Responses: untagged responses: FETCH, SEARCH
Result: OK - UID command completed
NO - UID command error
BAD - command unknown or arguments invalid
The UID command has two forms. In the first form, it takes as its
arguments a COPY, FETCH, or STORE command with arguments
appropriate for the associated command. However, the numbers in
the sequence set argument are unique identifiers instead of
message sequence numbers. Sequence set ranges are permitted, but
there is no guarantee that unique identifiers will be contiguous.
A non-existent unique identifier is ignored without any error
message generated. Thus, it is possible for a UID FETCH command
to return an OK without any data or a UID COPY or UID STORE to
return an OK without performing any operations.
In the second form, the UID command takes a SEARCH command with
SEARCH command arguments. The interpretation of the arguments is
the same as with SEARCH; however, the numbers returned in a SEARCH
response for a UID SEARCH command are unique identifiers instead
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of message sequence numbers. For example, the command UID SEARCH
1:100 UID 443:557 returns the unique identifiers corresponding to
the intersection of two sequence sets, the message sequence number
range 1:100 and the UID range 443:557.
Note: in the above example, the UID range 443:557
appears. The same comment about a non-existent unique
identifier being ignored without any error message also
applies here. Hence, even if neither UID 443 or 557
exist, this range is valid and would include an existing
UID 495.
Also note that a UID range of 559:* always includes the
UID of the last message in the mailbox, even if 559 is
higher than any assigned UID value. This is because the
contents of a range are independent of the order of the
range endpoints. Thus, any UID range with * as one of
the endpoints indicates at least one message (the
message with the highest numbered UID), unless the
mailbox is empty.
The number after the "*" in an untagged FETCH response is always a
message sequence number, not a unique identifier, even for a UID
command response. However, server implementations MUST implicitly
include the UID message data item as part of any FETCH response
caused by a UID command, regardless of whether a UID was specified
as a message data item to the FETCH.
Note: The rule about including the UID message data item as part
of a FETCH response primarily applies to the UID FETCH and UID
STORE commands, including a UID FETCH command that does not
include UID as a message data item. Although it is unlikely that
the other UID commands will cause an untagged FETCH, this rule
applies to these commands as well.
Example: C: A999 UID FETCH 4827313:4828442 FLAGS
S: * 23 FETCH (FLAGS (\Seen) UID 4827313)
S: * 24 FETCH (FLAGS (\Seen) UID 4827943)
S: * 25 FETCH (FLAGS (\Seen) UID 4828442)
S: A999 OK UID FETCH completed
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6.5. Client Commands - Experimental/Expansion
6.5.1. X<atom> Command
Arguments: implementation defined
Responses: implementation defined
Result: OK - command completed
NO - failure
BAD - command unknown or arguments invalid
Any command prefixed with an X is an experimental command.
Commands which are not part of this specification, a standard or
standards-track revision of this specification, or an
IESG-approved experimental protocol, MUST use the X prefix.
Any added untagged responses issued by an experimental command
MUST also be prefixed with an X. Server implementations MUST NOT
send any such untagged responses, unless the client requested it
by issuing the associated experimental command.
Example: C: a441 CAPABILITY
S: * CAPABILITY IMAP4rev1 XPIG-LATIN
S: a441 OK CAPABILITY completed
C: A442 XPIG-LATIN
S: * XPIG-LATIN ow-nay eaking-spay ig-pay atin-lay
S: A442 OK XPIG-LATIN ompleted-cay
7. Server Responses
Server responses are in three forms: status responses, server data,
and command continuation request. The information contained in a
server response, identified by "Contents:" in the response
descriptions below, is described by function, not by syntax. The
precise syntax of server responses is described in the Formal Syntax
section.
The client MUST be prepared to accept any response at all times.
Status responses can be tagged or untagged. Tagged status responses
indicate the completion result (OK, NO, or BAD status) of a client
command, and have a tag matching the command.
Some status responses, and all server data, are untagged. An
untagged response is indicated by the token "*" instead of a tag.
Untagged status responses indicate server greeting, or server status
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that does not indicate the completion of a command (for example, an
impending system shutdown alert). For historical reasons, untagged
server data responses are also called "unsolicited data", although
strictly speaking, only unilateral server data is truly
"unsolicited".
Certain server data MUST be recorded by the client when it is
received; this is noted in the description of that data. Such data
conveys critical information which affects the interpretation of all
subsequent commands and responses (e.g., updates reflecting the
creation or destruction of messages).
Other server data SHOULD be recorded for later reference; if the
client does not need to record the data, or if recording the data has
no obvious purpose (e.g., a SEARCH response when no SEARCH command is
in progress), the data SHOULD be ignored.
An example of unilateral untagged server data occurs when the IMAP
connection is in the selected state. In the selected state, the
server checks the mailbox for new messages as part of command
execution. Normally, this is part of the execution of every command;
hence, a NOOP command suffices to check for new messages. If new
messages are found, the server sends untagged EXISTS and RECENT
responses reflecting the new size of the mailbox. Server
implementations that offer multiple simultaneous access to the same
mailbox SHOULD also send appropriate unilateral untagged FETCH and
EXPUNGE responses if another agent changes the state of any message
flags or expunges any messages.
Command continuation request responses use the token "+" instead of a
tag. These responses are sent by the server to indicate acceptance
of an incomplete client command and readiness for the remainder of
the command.
7.1. Server Responses - Status Responses
Status responses are OK, NO, BAD, PREAUTH and BYE. OK, NO, and BAD
can be tagged or untagged. PREAUTH and BYE are always untagged.
Status responses MAY include an OPTIONAL "response code". A response
code consists of data inside square brackets in the form of an atom,
possibly followed by a space and arguments. The response code
contains additional information or status codes for client software
beyond the OK/NO/BAD condition, and are defined when there is a
specific action that a client can take based upon the additional
information.
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The currently defined response codes are:
ALERT
The human-readable text contains a special alert that MUST be
presented to the user in a fashion that calls the user's
attention to the message.
BADCHARSET
Optionally followed by a parenthesized list of charsets. A
SEARCH failed because the given charset is not supported by
this implementation. If the optional list of charsets is
given, this lists the charsets that are supported by this
implementation.
CAPABILITY
Followed by a list of capabilities. This can appear in the
initial OK or PREAUTH response to transmit an initial
capabilities list. This makes it unnecessary for a client to
send a separate CAPABILITY command if it recognizes this
response.
PARSE
The human-readable text represents an error in parsing the
[RFC-2822] header or [MIME-IMB] headers of a message in the
mailbox.
PERMANENTFLAGS
Followed by a parenthesized list of flags, indicates which of
the known flags the client can change permanently. Any flags
that are in the FLAGS untagged response, but not the
PERMANENTFLAGS list, can not be set permanently. If the client
attempts to STORE a flag that is not in the PERMANENTFLAGS
list, the server will either ignore the change or store the
state change for the remainder of the current session only.
The PERMANENTFLAGS list can also include the special flag \*,
which indicates that it is possible to create new keywords by
attempting to store those flags in the mailbox.
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READ-ONLY
The mailbox is selected read-only, or its access while selected
has changed from read-write to read-only.
READ-WRITE
The mailbox is selected read-write, or its access while
selected has changed from read-only to read-write.
TRYCREATE
An APPEND or COPY attempt is failing because the target mailbox
does not exist (as opposed to some other reason). This is a
hint to the client that the operation can succeed if the
mailbox is first created by the CREATE command.
UIDNEXT
Followed by a decimal number, indicates the next unique
identifier value. Refer to section 2.3.1.1 for more
information.
UIDVALIDITY
Followed by a decimal number, indicates the unique identifier
validity value. Refer to section 2.3.1.1 for more information.
UNSEEN
Followed by a decimal number, indicates the number of the first
message without the \Seen flag set.
Additional response codes defined by particular client or server
implementations SHOULD be prefixed with an "X" until they are
added to a revision of this protocol. Client implementations
SHOULD ignore response codes that they do not recognize.
7.1.1. OK Response
Contents: OPTIONAL response code
human-readable text
The OK response indicates an information message from the server.
When tagged, it indicates successful completion of the associated
command. The human-readable text MAY be presented to the user as
an information message. The untagged form indicates an
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information-only message; the nature of the information MAY be
indicated by a response code.
The untagged form is also used as one of three possible greetings
at connection startup. It indicates that the connection is not
yet authenticated and that a LOGIN command is needed.
Example: S: * OK IMAP4rev1 server ready
C: A001 LOGIN fred blurdybloop
S: * OK [ALERT] System shutdown in 10 minutes
S: A001 OK LOGIN Completed
7.1.2. NO Response
Contents: OPTIONAL response code
human-readable text
The NO response indicates an operational error message from the
server. When tagged, it indicates unsuccessful completion of the
associated command. The untagged form indicates a warning; the
command can still complete successfully. The human-readable text
describes the condition.
Example: C: A222 COPY 1:2 owatagusiam
S: * NO Disk is 98% full, please delete unnecessary data
S: A222 OK COPY completed
C: A223 COPY 3:200 blurdybloop
S: * NO Disk is 98% full, please delete unnecessary data
S: * NO Disk is 99% full, please delete unnecessary data
S: A223 NO COPY failed: disk is full
7.1.3. BAD Response
Contents: OPTIONAL response code
human-readable text
The BAD response indicates an error message from the server. When
tagged, it reports a protocol-level error in the client's command;
the tag indicates the command that caused the error. The untagged
form indicates a protocol-level error for which the associated
command can not be determined; it can also indicate an internal
server failure. The human-readable text describes the condition.
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Example: C: ...very long command line...
S: * BAD Command line too long
C: ...empty line...
S: * BAD Empty command line
C: A443 EXPUNGE
S: * BAD Disk crash, attempting salvage to a new disk!
S: * OK Salvage successful, no data lost
S: A443 OK Expunge completed
7.1.4. PREAUTH Response
Contents: OPTIONAL response code
human-readable text
The PREAUTH response is always untagged, and is one of three
possible greetings at connection startup. It indicates that the
connection has already been authenticated by external means; thus
no LOGIN command is needed.
Example: S: * PREAUTH IMAP4rev1 server logged in as Smith
7.1.5. BYE Response
Contents: OPTIONAL response code
human-readable text
The BYE response is always untagged, and indicates that the server
is about to close the connection. The human-readable text MAY be
displayed to the user in a status report by the client. The BYE
response is sent under one of four conditions:
1) as part of a normal logout sequence. The server will close
the connection after sending the tagged OK response to the
LOGOUT command.
2) as a panic shutdown announcement. The server closes the
connection immediately.
3) as an announcement of an inactivity autologout. The server
closes the connection immediately.
4) as one of three possible greetings at connection startup,
indicating that the server is not willing to accept a
connection from this client. The server closes the
connection immediately.
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The difference between a BYE that occurs as part of a normal
LOGOUT sequence (the first case) and a BYE that occurs because of
a failure (the other three cases) is that the connection closes
immediately in the failure case. In all cases the client SHOULD
continue to read response data from the server until the
connection is closed; this will ensure that any pending untagged
or completion responses are read and processed.
Example: S: * BYE Autologout; idle for too long
7.2. Server Responses - Server and Mailbox Status
These responses are always untagged. This is how server and mailbox
status data are transmitted from the server to the client. Many of
these responses typically result from a command with the same name.
7.2.1. CAPABILITY Response
Contents: capability listing
The CAPABILITY response occurs as a result of a CAPABILITY
command. The capability listing contains a space-separated
listing of capability names that the server supports. The
capability listing MUST include the atom "IMAP4rev1".
In addition, client and server implementations MUST implement the
STARTTLS, LOGINDISABLED, and AUTH=PLAIN (described in [IMAP-TLS])
capabilities. See the Security Considerations section for
important information.
A capability name which begins with "AUTH=" indicates that the
server supports that particular authentication mechanism.
The LOGINDISABLED capability indicates that the LOGIN command is
disabled, and that the server will respond with a tagged NO
response to any attempt to use the LOGIN command even if the user
name and password are valid. An IMAP client MUST NOT issue the
LOGIN command if the server advertises the LOGINDISABLED
capability.
Other capability names indicate that the server supports an
extension, revision, or amendment to the IMAP4rev1 protocol.
Server responses MUST conform to this document until the client
issues a command that uses the associated capability.
Capability names MUST either begin with "X" or be standard or
standards-track IMAP4rev1 extensions, revisions, or amendments
registered with IANA. A server MUST NOT offer unregistered or
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RFC 3501 IMAPv4 March 2003
non-standard capability names, unless such names are prefixed with
an "X".
Client implementations SHOULD NOT require any capability name
other than "IMAP4rev1", and MUST ignore any unknown capability
names.
A server MAY send capabilities automatically, by using the
CAPABILITY response code in the initial PREAUTH or OK responses,
and by sending an updated CAPABILITY response code in the tagged
OK response as part of a successful authentication. It is
unnecessary for a client to send a separate CAPABILITY command if
it recognizes these automatic capabilities.
Example: S: * CAPABILITY IMAP4rev1 STARTTLS AUTH=GSSAPI XPIG-LATIN
7.2.2. LIST Response
Contents: name attributes
hierarchy delimiter
name
The LIST response occurs as a result of a LIST command. It
returns a single name that matches the LIST specification. There
can be multiple LIST responses for a single LIST command.
Four name attributes are defined:
\Noinferiors
It is not possible for any child levels of hierarchy to exist
under this name; no child levels exist now and none can be
created in the future.
\Noselect
It is not possible to use this name as a selectable mailbox.
\Marked
The mailbox has been marked "interesting" by the server; the
mailbox probably contains messages that have been added since
the last time the mailbox was selected.
\Unmarked
The mailbox does not contain any additional messages since the
last time the mailbox was selected.
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If it is not feasible for the server to determine whether or not
the mailbox is "interesting", or if the name is a \Noselect name,
the server SHOULD NOT send either \Marked or \Unmarked.
The hierarchy delimiter is a character used to delimit levels of
hierarchy in a mailbox name. A client can use it to create child
mailboxes, and to search higher or lower levels of naming
hierarchy. All children of a top-level hierarchy node MUST use
the same separator character. A NIL hierarchy delimiter means
that no hierarchy exists; the name is a "flat" name.
The name represents an unambiguous left-to-right hierarchy, and
MUST be valid for use as a reference in LIST and LSUB commands.
Unless \Noselect is indicated, the name MUST also be valid as an
argument for commands, such as SELECT, that accept mailbox names.
Example: S: * LIST (\Noselect) "/" ~/Mail/foo
7.2.3. LSUB Response
Contents: name attributes
hierarchy delimiter
name
The LSUB response occurs as a result of an LSUB command. It
returns a single name that matches the LSUB specification. There
can be multiple LSUB responses for a single LSUB command. The
data is identical in format to the LIST response.
Example: S: * LSUB () "." #news.comp.mail.misc
7.2.4 STATUS Response
Contents: name
status parenthesized list
The STATUS response occurs as a result of an STATUS command. It
returns the mailbox name that matches the STATUS specification and
the requested mailbox status information.
Example: S: * STATUS blurdybloop (MESSAGES 231 UIDNEXT 44292)
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7.2.5. SEARCH Response
Contents: zero or more numbers
The SEARCH response occurs as a result of a SEARCH or UID SEARCH
command. The number(s) refer to those messages that match the
search criteria. For SEARCH, these are message sequence numbers;
for UID SEARCH, these are unique identifiers. Each number is
delimited by a space.
Example: S: * SEARCH 2 3 6
7.2.6. FLAGS Response
Contents: flag parenthesized list
The FLAGS response occurs as a result of a SELECT or EXAMINE
command. The flag parenthesized list identifies the flags (at a
minimum, the system-defined flags) that are applicable for this
mailbox. Flags other than the system flags can also exist,
depending on server implementation.
The update from the FLAGS response MUST be recorded by the client.
Example: S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
7.3. Server Responses - Mailbox Size
These responses are always untagged. This is how changes in the size
of the mailbox are transmitted from the server to the client.
Immediately following the "*" token is a number that represents a
message count.
7.3.1. EXISTS Response
Contents: none
The EXISTS response reports the number of messages in the mailbox.
This response occurs as a result of a SELECT or EXAMINE command,
and if the size of the mailbox changes (e.g., new messages).
The update from the EXISTS response MUST be recorded by the
client.
Example: S: * 23 EXISTS
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7.3.2. RECENT Response
Contents: none
The RECENT response reports the number of messages with the
\Recent flag set. This response occurs as a result of a SELECT or
EXAMINE command, and if the size of the mailbox changes (e.g., new
messages).
Note: It is not guaranteed that the message sequence
numbers of recent messages will be a contiguous range of
the highest n messages in the mailbox (where n is the
value reported by the RECENT response). Examples of
situations in which this is not the case are: multiple
clients having the same mailbox open (the first session
to be notified will see it as recent, others will
probably see it as non-recent), and when the mailbox is
re-ordered by a non-IMAP agent.
The only reliable way to identify recent messages is to
look at message flags to see which have the \Recent flag
set, or to do a SEARCH RECENT.
The update from the RECENT response MUST be recorded by the
client.
Example: S: * 5 RECENT
7.4. Server Responses - Message Status
These responses are always untagged. This is how message data are
transmitted from the server to the client, often as a result of a
command with the same name. Immediately following the "*" token is a
number that represents a message sequence number.
7.4.1. EXPUNGE Response
Contents: none
The EXPUNGE response reports that the specified message sequence
number has been permanently removed from the mailbox. The message
sequence number for each successive message in the mailbox is
immediately decremented by 1, and this decrement is reflected in
message sequence numbers in subsequent responses (including other
untagged EXPUNGE responses).
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The EXPUNGE response also decrements the number of messages in the
mailbox; it is not necessary to send an EXISTS response with the
new value.
As a result of the immediate decrement rule, message sequence
numbers that appear in a set of successive EXPUNGE responses
depend upon whether the messages are removed starting from lower
numbers to higher numbers, or from higher numbers to lower
numbers. For example, if the last 5 messages in a 9-message
mailbox are expunged, a "lower to higher" server will send five
untagged EXPUNGE responses for message sequence number 5, whereas
a "higher to lower server" will send successive untagged EXPUNGE
responses for message sequence numbers 9, 8, 7, 6, and 5.
An EXPUNGE response MUST NOT be sent when no command is in
progress, nor while responding to a FETCH, STORE, or SEARCH
command. This rule is necessary to prevent a loss of
synchronization of message sequence numbers between client and
server. A command is not "in progress" until the complete command
has been received; in particular, a command is not "in progress"
during the negotiation of command continuation.
Note: UID FETCH, UID STORE, and UID SEARCH are different
commands from FETCH, STORE, and SEARCH. An EXPUNGE
response MAY be sent during a UID command.
The update from the EXPUNGE response MUST be recorded by the
client.
Example: S: * 44 EXPUNGE
7.4.2. FETCH Response
Contents: message data
The FETCH response returns data about a message to the client.
The data are pairs of data item names and their values in
parentheses. This response occurs as the result of a FETCH or
STORE command, as well as by unilateral server decision (e.g.,
flag updates).
The current data items are:
BODY
A form of BODYSTRUCTURE without extension data.
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BODY[<section>]<<origin octet>>
A string expressing the body contents of the specified section.
The string SHOULD be interpreted by the client according to the
content transfer encoding, body type, and subtype.
If the origin octet is specified, this string is a substring of
the entire body contents, starting at that origin octet. This
means that BODY[]<0> MAY be truncated, but BODY[] is NEVER
truncated.
Note: The origin octet facility MUST NOT be used by a server
in a FETCH response unless the client specifically requested
it by means of a FETCH of a BODY[<section>]<<partial>> data
item.
8-bit textual data is permitted if a [CHARSET] identifier is
part of the body parameter parenthesized list for this section.
Note that headers (part specifiers HEADER or MIME, or the
header portion of a MESSAGE/RFC822 part), MUST be 7-bit; 8-bit
characters are not permitted in headers. Note also that the
[RFC-2822] delimiting blank line between the header and the
body is not affected by header line subsetting; the blank line
is always included as part of header data, except in the case
of a message which has no body and no blank line.
Non-textual data such as binary data MUST be transfer encoded
into a textual form, such as BASE64, prior to being sent to the
client. To derive the original binary data, the client MUST
decode the transfer encoded string.
BODYSTRUCTURE
A parenthesized list that describes the [MIME-IMB] body
structure of a message. This is computed by the server by
parsing the [MIME-IMB] header fields, defaulting various fields
as necessary.
For example, a simple text message of 48 lines and 2279 octets
can have a body structure of: ("TEXT" "PLAIN" ("CHARSET"
"US-ASCII") NIL NIL "7BIT" 2279 48)
Multiple parts are indicated by parenthesis nesting. Instead
of a body type as the first element of the parenthesized list,
there is a sequence of one or more nested body structures. The
second element of the parenthesized list is the multipart
subtype (mixed, digest, parallel, alternative, etc.).
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For example, a two part message consisting of a text and a
BASE64-encoded text attachment can have a body structure of:
(("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152
23)("TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "cc.diff")
"<960723163407.20117h@cac.washington.edu>" "Compiler diff"
"BASE64" 4554 73) "MIXED")
Extension data follows the multipart subtype. Extension data
is never returned with the BODY fetch, but can be returned with
a BODYSTRUCTURE fetch. Extension data, if present, MUST be in
the defined order. The extension data of a multipart body part
are in the following order:
body parameter parenthesized list
A parenthesized list of attribute/value pairs [e.g., ("foo"
"bar" "baz" "rag") where "bar" is the value of "foo", and
"rag" is the value of "baz"] as defined in [MIME-IMB].
body disposition
A parenthesized list, consisting of a disposition type
string, followed by a parenthesized list of disposition
attribute/value pairs as defined in [DISPOSITION].
body language
A string or parenthesized list giving the body language
value as defined in [LANGUAGE-TAGS].
body location
A string list giving the body content URI as defined in
[LOCATION].
Any following extension data are not yet defined in this
version of the protocol. Such extension data can consist of
zero or more NILs, strings, numbers, or potentially nested
parenthesized lists of such data. Client implementations that
do a BODYSTRUCTURE fetch MUST be prepared to accept such
extension data. Server implementations MUST NOT send such
extension data until it has been defined by a revision of this
protocol.
The basic fields of a non-multipart body part are in the
following order:
body type
A string giving the content media type name as defined in
[MIME-IMB].
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body subtype
A string giving the content subtype name as defined in
[MIME-IMB].
body parameter parenthesized list
A parenthesized list of attribute/value pairs [e.g., ("foo"
"bar" "baz" "rag") where "bar" is the value of "foo" and
"rag" is the value of "baz"] as defined in [MIME-IMB].
body id
A string giving the content id as defined in [MIME-IMB].
body description
A string giving the content description as defined in
[MIME-IMB].
body encoding
A string giving the content transfer encoding as defined in
[MIME-IMB].
body size
A number giving the size of the body in octets. Note that
this size is the size in its transfer encoding and not the
resulting size after any decoding.
A body type of type MESSAGE and subtype RFC822 contains,
immediately after the basic fields, the envelope structure,
body structure, and size in text lines of the encapsulated
message.
A body type of type TEXT contains, immediately after the basic
fields, the size of the body in text lines. Note that this
size is the size in its content transfer encoding and not the
resulting size after any decoding.
Extension data follows the basic fields and the type-specific
fields listed above. Extension data is never returned with the
BODY fetch, but can be returned with a BODYSTRUCTURE fetch.
Extension data, if present, MUST be in the defined order.
The extension data of a non-multipart body part are in the
following order:
body MD5
A string giving the body MD5 value as defined in [MD5].
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body disposition
A parenthesized list with the same content and function as
the body disposition for a multipart body part.
body language
A string or parenthesized list giving the body language
value as defined in [LANGUAGE-TAGS].
body location
A string list giving the body content URI as defined in
[LOCATION].
Any following extension data are not yet defined in this
version of the protocol, and would be as described above under
multipart extension data.
ENVELOPE
A parenthesized list that describes the envelope structure of a
message. This is computed by the server by parsing the
[RFC-2822] header into the component parts, defaulting various
fields as necessary.
The fields of the envelope structure are in the following
order: date, subject, from, sender, reply-to, to, cc, bcc,
in-reply-to, and message-id. The date, subject, in-reply-to,
and message-id fields are strings. The from, sender, reply-to,
to, cc, and bcc fields are parenthesized lists of address
structures.
An address structure is a parenthesized list that describes an
electronic mail address. The fields of an address structure
are in the following order: personal name, [SMTP]
at-domain-list (source route), mailbox name, and host name.
[RFC-2822] group syntax is indicated by a special form of
address structure in which the host name field is NIL. If the
mailbox name field is also NIL, this is an end of group marker
(semi-colon in RFC 822 syntax). If the mailbox name field is
non-NIL, this is a start of group marker, and the mailbox name
field holds the group name phrase.
If the Date, Subject, In-Reply-To, and Message-ID header lines
are absent in the [RFC-2822] header, the corresponding member
of the envelope is NIL; if these header lines are present but
empty the corresponding member of the envelope is the empty
string.
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Note: some servers may return a NIL envelope member in the
"present but empty" case. Clients SHOULD treat NIL and
empty string as identical.
Note: [RFC-2822] requires that all messages have a valid
Date header. Therefore, the date member in the envelope can
not be NIL or the empty string.
Note: [RFC-2822] requires that the In-Reply-To and
Message-ID headers, if present, have non-empty content.
Therefore, the in-reply-to and message-id members in the
envelope can not be the empty string.
If the From, To, cc, and bcc header lines are absent in the
[RFC-2822] header, or are present but empty, the corresponding
member of the envelope is NIL.
If the Sender or Reply-To lines are absent in the [RFC-2822]
header, or are present but empty, the server sets the
corresponding member of the envelope to be the same value as
the from member (the client is not expected to know to do
this).
Note: [RFC-2822] requires that all messages have a valid
From header. Therefore, the from, sender, and reply-to
members in the envelope can not be NIL.
FLAGS
A parenthesized list of flags that are set for this message.
INTERNALDATE
A string representing the internal date of the message.
RFC822
Equivalent to BODY[].
RFC822.HEADER
Equivalent to BODY[HEADER]. Note that this did not result in
\Seen being set, because RFC822.HEADER response data occurs as
a result of a FETCH of RFC822.HEADER. BODY[HEADER] response
data occurs as a result of a FETCH of BODY[HEADER] (which sets
\Seen) or BODY.PEEK[HEADER] (which does not set \Seen).
RFC822.SIZE
A number expressing the [RFC-2822] size of the message.
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RFC822.TEXT
Equivalent to BODY[TEXT].
UID
A number expressing the unique identifier of the message.
Example: S: * 23 FETCH (FLAGS (\Seen) RFC822.SIZE 44827)
7.5. Server Responses - Command Continuation Request
The command continuation request response is indicated by a "+" token
instead of a tag. This form of response indicates that the server is
ready to accept the continuation of a command from the client. The
remainder of this response is a line of text.
This response is used in the AUTHENTICATE command to transmit server
data to the client, and request additional client data. This
response is also used if an argument to any command is a literal.
The client is not permitted to send the octets of the literal unless
the server indicates that it is expected. This permits the server to
process commands and reject errors on a line-by-line basis. The
remainder of the command, including the CRLF that terminates a
command, follows the octets of the literal. If there are any
additional command arguments, the literal octets are followed by a
space and those arguments.
Example: C: A001 LOGIN {11}
S: + Ready for additional command text
C: FRED FOOBAR {7}
S: + Ready for additional command text
C: fat man
S: A001 OK LOGIN completed
C: A044 BLURDYBLOOP {102856}
S: A044 BAD No such command as "BLURDYBLOOP"
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9. Formal Syntax
The following syntax specification uses the Augmented Backus-Naur
Form (ABNF) notation as specified in [ABNF].
In the case of alternative or optional rules in which a later rule
overlaps an earlier rule, the rule which is listed earlier MUST take
priority. For example, "\Seen" when parsed as a flag is the \Seen
flag name and not a flag-extension, even though "\Seen" can be parsed
as a flag-extension. Some, but not all, instances of this rule are
noted below.
Note: [ABNF] rules MUST be followed strictly; in
particular:
(1) Except as noted otherwise, all alphabetic characters
are case-insensitive. The use of upper or lower case
characters to define token strings is for editorial clarity
only. Implementations MUST accept these strings in a
case-insensitive fashion.
(2) In all cases, SP refers to exactly one space. It is
NOT permitted to substitute TAB, insert additional spaces,
or otherwise treat SP as being equivalent to LWSP.
(3) The ASCII NUL character, %x00, MUST NOT be used at any
time.
address = "(" addr-name SP addr-adl SP addr-mailbox SP
addr-host ")"
addr-adl = nstring
; Holds route from [RFC-2822] route-addr if
; non-NIL
addr-host = nstring
; NIL indicates [RFC-2822] group syntax.
; Otherwise, holds [RFC-2822] domain name
addr-mailbox = nstring
; NIL indicates end of [RFC-2822] group; if
; non-NIL and addr-host is NIL, holds
; [RFC-2822] group name.
; Otherwise, holds [RFC-2822] local-part
; after removing [RFC-2822] quoting
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section-spec = section-msgtext / (section-part ["." section-text])
section-text = section-msgtext / "MIME"
; text other than actual body part (headers, etc.)
select = "SELECT" SP mailbox
seq-number = nz-number / "*"
; message sequence number (COPY, FETCH, STORE
; commands) or unique identifier (UID COPY,
; UID FETCH, UID STORE commands).
; * represents the largest number in use. In
; the case of message sequence numbers, it is
; the number of messages in a non-empty mailbox.
; In the case of unique identifiers, it is the
; unique identifier of the last message in the
; mailbox or, if the mailbox is empty, the
; mailbox's current UIDNEXT value.
; The server should respond with a tagged BAD
; response to a command that uses a message
; sequence number greater than the number of
; messages in the selected mailbox. This
; includes "*" if the selected mailbox is empty.
seq-range = seq-number ":" seq-number
; two seq-number values and all values between
; these two regardless of order.
; Example: 2:4 and 4:2 are equivalent and indicate
; values 2, 3, and 4.
; Example: a unique identifier sequence range of
; 3291:* includes the UID of the last message in
; the mailbox, even if that value is less than 3291.
sequence-set = (seq-number / seq-range) *("," sequence-set)
; set of seq-number values, regardless of order.
; Servers MAY coalesce overlaps and/or execute the
; sequence in any order.
; Example: a message sequence number set of
; 2,4:7,9,12:* for a mailbox with 15 messages is
; equivalent to 2,4,5,6,7,9,12,13,14,15
; Example: a message sequence number set of *:4,5:7
; for a mailbox with 10 messages is equivalent to
; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and
; overlap coalesced to be 4,5,6,7,8,9,10.
status = "STATUS" SP mailbox SP
"(" status-att *(SP status-att) ")"
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RFC 3501 IMAPv4 March 2003
10. Author's Note
This document is a revision or rewrite of earlier documents, and
supercedes the protocol specification in those documents: RFC 2060,
RFC 1730, unpublished IMAP2bis.TXT document, RFC 1176, and RFC 1064.
11. Security Considerations
IMAP4rev1 protocol transactions, including electronic mail data, are
sent in the clear over the network unless protection from snooping is
negotiated. This can be accomplished either by the use of STARTTLS,
negotiated privacy protection in the AUTHENTICATE command, or some
other protection mechanism.
11.1. STARTTLS Security Considerations
The specification of the STARTTLS command and LOGINDISABLED
capability in this document replaces that in [IMAP-TLS]. [IMAP-TLS]
remains normative for the PLAIN [SASL] authenticator.
IMAP client and server implementations MUST implement the
TLS_RSA_WITH_RC4_128_MD5 [TLS] cipher suite, and SHOULD implement the
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA [TLS] cipher suite. This is
important as it assures that any two compliant implementations can be
configured to interoperate. All other cipher suites are OPTIONAL.
Note that this is a change from section 2.1 of [IMAP-TLS].
During the [TLS] negotiation, the client MUST check its understanding
of the server hostname against the server's identity as presented in
the server Certificate message, in order to prevent man-in-the-middle
attacks. If the match fails, the client SHOULD either ask for
explicit user confirmation, or terminate the connection and indicate
that the server's identity is suspect. Matching is performed
according to these rules:
The client MUST use the server hostname it used to open the
connection as the value to compare against the server name
as expressed in the server certificate. The client MUST
NOT use any form of the server hostname derived from an
insecure remote source (e.g., insecure DNS lookup). CNAME
canonicalization is not done.
If a subjectAltName extension of type dNSName is present in
the certificate, it SHOULD be used as the source of the
server's identity.
Matching is case-insensitive.
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RFC 3501 IMAPv4 March 2003
A "*" wildcard character MAY be used as the left-most name
component in the certificate. For example, *.example.com
would match a.example.com, foo.example.com, etc. but would
not match example.com.
If the certificate contains multiple names (e.g., more than
one dNSName field), then a match with any one of the fields
is considered acceptable.
Both the client and server MUST check the result of the STARTTLS
command and subsequent [TLS] negotiation to see whether acceptable
authentication or privacy was achieved.
11.2. Other Security Considerations
A server error message for an AUTHENTICATE command which fails due to
invalid credentials SHOULD NOT detail why the credentials are
invalid.
Use of the LOGIN command sends passwords in the clear. This can be
avoided by using the AUTHENTICATE command with a [SASL] mechanism
that does not use plaintext passwords, by first negotiating
encryption via STARTTLS or some other protection mechanism.
A server implementation MUST implement a configuration that, at the
time of authentication, requires:
(1) The STARTTLS command has been negotiated.
OR
(2) Some other mechanism that protects the session from password
snooping has been provided.
OR
(3) The following measures are in place:
(a) The LOGINDISABLED capability is advertised, and [SASL]
mechanisms (such as PLAIN) using plaintext passwords are NOT
advertised in the CAPABILITY list.
AND
(b) The LOGIN command returns an error even if the password is
correct.
AND
(c) The AUTHENTICATE command returns an error with all [SASL]
mechanisms that use plaintext passwords, even if the password
is correct.
A server error message for a failing LOGIN command SHOULD NOT specify
that the user name, as opposed to the password, is invalid.
A server SHOULD have mechanisms in place to limit or delay failed
AUTHENTICATE/LOGIN attempts.
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RFC 3501 IMAPv4 March 2003
Additional security considerations are discussed in the section
discussing the AUTHENTICATE and LOGIN commands.
12. IANA Considerations
IMAP4 capabilities are registered by publishing a standards track or
IESG approved experimental RFC. The registry is currently located
at:
http://www.iana.org/assignments/imap4-capabilities
As this specification revises the STARTTLS and LOGINDISABLED
extensions previously defined in [IMAP-TLS], the registry will be
updated accordingly.
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9) Remove obsolete "MAILBOX" response from mailbox-data.
10) A spurious "<" in the rule for mailbox-data was removed.
11) Add CRLF to continue-req.
12) Specifically exclude "]" from the atom in resp-text-code.
13) Clarify that clients and servers should adhere strictly to the
protocol syntax.
14) Emphasize in 5.2 that EXISTS can not be used to shrink a mailbox.
15) Add NEWNAME to resp-text-code.
16) Clarify that the empty string, not NIL, is used as arguments to
LIST.
17) Clarify that NIL can be returned as a hierarchy delimiter for the
empty string mailbox name argument if the mailbox namespace is flat.
18) Clarify that addr-mailbox and addr-name have RFC-2822 quoting
removed.
19) Update UTF-7 reference.
20) Fix example in 6.3.11.
21) Clarify that non-existent UIDs are ignored.
22) Update DISPOSITION reference.
23) Expand state diagram.
24) Clarify that partial fetch responses are only returned in
response to a partial fetch command.
25) Add UIDNEXT response code. Correct UIDVALIDITY definition
reference.
26) Further clarification of "can" vs. "MAY".
27) Reference RFC-2119.
28) Clarify that superfluous shifts are not permitted in modified
UTF-7.
29) Clarify that there are no implicit shifts in modified UTF-7.
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RFC 3501 IMAPv4 March 2003
30) Clarify that "INBOX" in a mailbox name is always INBOX, even if
it is given as a string.
31) Add missing open parenthesis in media-basic grammar rule.
32) Correct attribute syntax in mailbox-data.
33) Add UIDNEXT to EXAMINE responses.
34) Clarify UNSEEN, PERMANENTFLAGS, UIDVALIDITY, and UIDNEXT
responses in SELECT and EXAMINE. They are required now, but weren't
in older versions.
35) Update references with RFC numbers.
36) Flush text-mime2.
37) Clarify that modified UTF-7 names must be case-sensitive and that
violating the convention should be avoided.
38) Correct UID FETCH example.
39) Clarify UID FETCH, UID STORE, and UID SEARCH vs. untagged EXPUNGE
responses.
40) Clarify the use of the word "convention".
41) Clarify that a command is not "in progress" until it has been
fully received (specifically, that a command is not "in progress"
during command continuation negotiation).
42) Clarify envelope defaulting.
43) Clarify that SP means one and only one space character.
44) Forbid silly states in LIST response.
45) Clarify that the ENVELOPE, INTERNALDATE, RFC822*, BODY*, and UID
for a message is static.
46) Add BADCHARSET response code.
47) Update formal syntax to [ABNF] conventions.
48) Clarify trailing hierarchy delimiter in CREATE semantics.
49) Clarify that the "blank line" is the [RFC-2822] delimiting blank
line.
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RFC 3501 IMAPv4 March 2003
50) Clarify that RENAME should also create hierarchy as needed for
the command to complete.
51) Fix body-ext-mpart to not require language if disposition
present.
52) Clarify the RFC822.HEADER response.
53) Correct missing space after charset astring in search.
54) Correct missing quote for BADCHARSET in resp-text-code.
55) Clarify that ALL, FAST, and FULL preclude any other data items
appearing.
56) Clarify semantics of reference argument in LIST.
57) Clarify that a null string for SEARCH HEADER X-FOO means any
message with a header line with a field-name of X-FOO regardless of
the text of the header.
58) Specifically reserve 8-bit mailbox names for future use as UTF-8.
59) It is not an error for the client to store a flag that is not in
the PERMANENTFLAGS list; however, the server will either ignore the
change or make the change in the session only.
60) Correct/clarify the text regarding superfluous shifts.
61) Correct typographic errors in the "Changes" section.
62) Clarify that STATUS must not be used to check for new messages in
the selected mailbox
63) Clarify LSUB behavior with "%" wildcard.
64) Change AUTHORIZATION to AUTHENTICATE in section 7.5.
65) Clarify description of multipart body type.
66) Clarify that STORE FLAGS does not affect \Recent.
67) Change "west" to "east" in description of timezone.
68) Clarify that commands which break command pipelining must wait
for a completion result response.
69) Clarify that EXAMINE does not affect \Recent.
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RFC 3501 IMAPv4 March 2003
70) Make description of MIME structure consistent.
71) Clarify that date searches disregard the time and timezone of the
INTERNALDATE or Date: header. In other words, "ON 13-APR-2000" means
messages with an INTERNALDATE text which starts with "13-APR-2000",
even if timezone differential from the local timezone is sufficient
to move that INTERNALDATE into the previous or next day.
72) Clarify that the header fetches don't add a blank line if one
isn't in the [RFC-2822] message.
73) Clarify (in discussion of UIDs) that messages are immutable.
74) Add an example of CHARSET searching.
75) Clarify in SEARCH that keywords are a type of flag.
76) Clarify the mandatory nature of the SELECT data responses.
77) Add optional CAPABILITY response code in the initial OK or
PREAUTH.
78) Add note that server can send an untagged CAPABILITY command as
part of the responses to AUTHENTICATE and LOGIN.
79) Remove statement about it being unnecessary to issue a CAPABILITY
command more than once in a connection. That statement is no longer
true.
80) Clarify that untagged EXPUNGE decrements the number of messages
in the mailbox.
81) Fix definition of "body" (concatenation has tighter binding than
alternation).
82) Add a new "Special Notes to Implementors" section with reference
to [IMAP-IMPLEMENTATION].
83) Clarify that an untagged CAPABILITY response to an AUTHENTICATE
command should only be done if a security layer was not negotiated.
84) Change the definition of atom to exclude "]". Update astring to
include "]" for compatibility with the past. Remove resp-text-atom.
85) Remove NEWNAME. It can't work because mailbox names can be
literals and can include "]". Functionality can be addressed via
referrals.
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RFC 3501 IMAPv4 March 2003
86) Move modified UTF-7 rationale in order to have more logical
paragraph flow.
87) Clarify UID uniqueness guarantees with the use of MUST.
88) Note that clients should read response data until the connection
is closed instead of immediately closing on a BYE.
89) Change RFC-822 references to RFC-2822.
90) Clarify that RFC-2822 should be followed instead of RFC-822.
91) Change recommendation of optional automatic capabilities in LOGIN
and AUTHENTICATE to use the CAPABILITY response code in the tagged
OK. This is more interoperable than an unsolicited untagged
CAPABILITY response.
92) STARTTLS and AUTH=PLAIN are mandatory to implement; add
recommendations for other [SASL] mechanisms.
93) Clarify that a "connection" (as opposed to "server" or "command")
is in one of the four states.
94) Clarify that a failed or rejected command does not change state.
95) Split references between normative and informative.
96) Discuss authentication failure issues in security section.
97) Clarify that a data item is not necessarily of only one data
type.
98) Clarify that sequence ranges are independent of order.
99) Change an example to clarify that superfluous shifts in
Modified-UTF7 can not be fixed just by omitting the shift. The
entire string must be recalculated.
100) Change Envelope Structure definition since [RFC-2822] uses
"envelope" to refer to the [SMTP] envelope and not the envelope data
that appears in the [RFC-2822] header.
101) Expand on RFC822.HEADER response data vs. BODY[HEADER].
102) Clarify Logout state semantics, change ASCII art.
103) Security changes to comply with IESG requirements.
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RFC 3501 IMAPv4 March 2003
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. v This
document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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